Drop support for old versions of Ruby

Drops support for Ruby 2.1 (EOL March 31, 2017) and 2.2 (EOL March 31,
2018). They're removed from `.travis.yml` and the gemspec and RuboCop
configuration have also been updated to the new lower bound.

Most of the diff here are minor updates to styling as required by
RuboCop:

* String literals are frozen by default, so the `.freeze` we had
  everywhere is now considered redundant.

* We can now use Ruby 1.9 style hash syntax with string keys like `{
  "foo": "bar" }.

* Converted a few heredocs over to use squiggly (leading whitespace
  removed) syntax.

As discussed in Slack, I didn't drop support for Ruby 2.2 (EOL March 31,
2019) as we still have quite a few users on it. As far as I know
dropping it doesn't get us access to any major syntax improvements or
anything, so it's probably not a big deal.

.rubocop.yml

@@ -2,7 +2,7 @@ inherit_from: .rubocop_todo.yml
 
 AllCops:
   DisplayCopNames: true
-  TargetRubyVersion: 2.1
+  TargetRubyVersion: 2.3
 
 Layout/CaseIndentation:
   EnforcedStyle: end
@@ -39,6 +39,9 @@ Style/AccessModifierDeclarations:
 Style/FrozenStringLiteralComment:
   EnforcedStyle: always
 
+Style/NumericPredicate:
+  Enabled: false
+
 Style/StringLiterals:
   EnforcedStyle: double_quotes
 

.rubocop_todo.yml

@@ -6,12 +6,6 @@
 # Note that changes in the inspected code, or installation of new
 # versions of RuboCop, may require this file to be generated again.
 
-Layout/ClosingHeredocIndentation:
-  # As far as I can tell, this lint rule just doesn't work when it comes to
-  # heredoc in `it` blocks.
-  Exclude:
-    - 'test/**/*'
-
 # Offense count: 20
 Metrics/AbcSize:
   Max: 53

.travis.yml

@@ -1,8 +1,6 @@
 language: ruby
 
 rvm:
-  - 2.1
-  - 2.2
   - 2.3
   - 2.4
   - 2.5

lib/stripe/list_object.rb

@@ -7,7 +7,7 @@ class ListObject < StripeObject
     include Stripe::APIOperations::Request
     include Stripe::APIOperations::Create
 
-    OBJECT_NAME = "list".freeze
+    OBJECT_NAME = "list"
 
     # This accessor allows a `ListObject` to inherit various filters that were
     # given to a predecessor. This allows for things like consistent limits,

lib/stripe/multipart_encoder.rb

@@ -16,7 +16,7 @@ module Stripe
   # placed in the `Content-Type` header of a subsequent request (which includes
   # a boundary value).
   class MultipartEncoder
-    MULTIPART_FORM_DATA = "multipart/form-data".freeze
+    MULTIPART_FORM_DATA = "multipart/form-data"
 
     # A shortcut for encoding a single set of parameters and finalizing a
     # result.
@@ -35,10 +35,9 @@ def self.encode(params)
 
     # Initializes a new multipart encoder.
     def initialize
-      # We seed this with an empty string so that it encoding defaults to UTF-8
-      # instead of ASCII. The empty string is UTF-8 and new string inherits the
-      # encoding of the string it's seeded with.
-      @body = String.new("")
+      # Kind of weird, but required by Rubocop because the unary plus operator
+      # is considered faster than `Stripe.new`.
+      @body = +""
 
       # Chose the same number of random bytes that Go uses in its standard
       # library implementation. Easily enough entropy to ensure that it won't

lib/stripe/resources/account.rb

@@ -9,7 +9,7 @@ class Account < APIResource
     include Stripe::APIOperations::Save
     extend Stripe::APIOperations::NestedResource
 
-    OBJECT_NAME = "account".freeze
+    OBJECT_NAME = "account"
 
     custom_method :reject, http_verb: :post
 

lib/stripe/resources/account_link.rb

@@ -4,6 +4,6 @@ module Stripe
   class AccountLink < APIResource
     extend Stripe::APIOperations::Create
 
-    OBJECT_NAME = "account_link".freeze
+    OBJECT_NAME = "account_link"
   end
 end

lib/stripe/resources/alipay_account.rb

@@ -5,7 +5,7 @@ class AlipayAccount < APIResource
     include Stripe::APIOperations::Save
     include Stripe::APIOperations::Delete
 
-    OBJECT_NAME = "alipay_account".freeze
+    OBJECT_NAME = "alipay_account"
 
     def resource_url
       if !respond_to?(:customer) || customer.nil?

lib/stripe/resources/apple_pay_domain.rb

@@ -7,7 +7,7 @@ class ApplePayDomain < APIResource
     include Stripe::APIOperations::Delete
     extend Stripe::APIOperations::List
 
-    OBJECT_NAME = "apple_pay_domain".freeze
+    OBJECT_NAME = "apple_pay_domain"
 
     def self.resource_url
       "/v1/apple_pay/domains"

lib/stripe/resources/application_fee.rb

@@ -5,7 +5,7 @@ class ApplicationFee < APIResource
     extend Stripe::APIOperations::List
     extend Stripe::APIOperations::NestedResource
 
-    OBJECT_NAME = "application_fee".freeze
+    OBJECT_NAME = "application_fee"
 
     nested_resource_class_methods :refund,
                                   operations: %i[create retrieve update list]

lib/stripe/resources/application_fee_refund.rb

@@ -5,7 +5,7 @@ class ApplicationFeeRefund < APIResource
     include Stripe::APIOperations::Save
     extend Stripe::APIOperations::List
 
-    OBJECT_NAME = "fee_refund".freeze
+    OBJECT_NAME = "fee_refund"
 
     def resource_url
       "#{ApplicationFee.resource_url}/#{CGI.escape(fee)}/refunds" \

lib/stripe/resources/balance.rb

@@ -2,6 +2,6 @@
 
 module Stripe
   class Balance < SingletonAPIResource
-    OBJECT_NAME = "balance".freeze
+    OBJECT_NAME = "balance"
   end
 end

lib/stripe/resources/balance_transaction.rb

@@ -4,7 +4,7 @@ module Stripe
   class BalanceTransaction < APIResource
     extend Stripe::APIOperations::List
 
-    OBJECT_NAME = "balance_transaction".freeze
+    OBJECT_NAME = "balance_transaction"
 
     def self.resource_url
       "/v1/balance/history"

lib/stripe/resources/bank_account.rb

@@ -6,7 +6,7 @@ class BankAccount < APIResource
     extend Stripe::APIOperations::List
     include Stripe::APIOperations::Save
 
-    OBJECT_NAME = "bank_account".freeze
+    OBJECT_NAME = "bank_account"
 
     def verify(params = {}, opts = {})
       resp, opts = request(:post, resource_url + "/verify", params, opts)

lib/stripe/resources/bitcoin_receiver.rb

@@ -6,7 +6,7 @@ module Stripe
   class BitcoinReceiver < APIResource
     extend Stripe::APIOperations::List
 
-    OBJECT_NAME = "bitcoin_receiver".freeze
+    OBJECT_NAME = "bitcoin_receiver"
 
     def self.resource_url
       "/v1/bitcoin/receivers"

lib/stripe/resources/bitcoin_transaction.rb

@@ -6,7 +6,7 @@ class BitcoinTransaction < APIResource
     # Sources API instead: https://stripe.com/docs/sources/bitcoin
     extend Stripe::APIOperations::List
 
-    OBJECT_NAME = "bitcoin_transaction".freeze
+    OBJECT_NAME = "bitcoin_transaction"
 
     def self.resource_url
       "/v1/bitcoin/transactions"

lib/stripe/resources/capability.rb

@@ -5,7 +5,7 @@ class Capability < APIResource
     extend Stripe::APIOperations::List
     include Stripe::APIOperations::Save
 
-    OBJECT_NAME = "capability".freeze
+    OBJECT_NAME = "capability"
 
     def resource_url
       if !respond_to?(:account) || account.nil?

lib/stripe/resources/card.rb

@@ -6,7 +6,7 @@ class Card < APIResource
     extend Stripe::APIOperations::List
     include Stripe::APIOperations::Save
 
-    OBJECT_NAME = "card".freeze
+    OBJECT_NAME = "card"
 
     def resource_url
       if respond_to?(:recipient) && !recipient.nil? && !recipient.empty?

lib/stripe/resources/charge.rb

@@ -6,7 +6,7 @@ class Charge < APIResource
     extend Stripe::APIOperations::List
     include Stripe::APIOperations::Save
 
-    OBJECT_NAME = "charge".freeze
+    OBJECT_NAME = "charge"
 
     custom_method :capture, http_verb: :post
 

lib/stripe/resources/checkout/session.rb

@@ -5,7 +5,7 @@ module Checkout
     class Session < APIResource
       extend Stripe::APIOperations::Create
 
-      OBJECT_NAME = "checkout.session".freeze
+      OBJECT_NAME = "checkout.session"
     end
   end
 end

lib/stripe/resources/country_spec.rb

@@ -4,6 +4,6 @@ module Stripe
   class CountrySpec < APIResource
     extend Stripe::APIOperations::List
 
-    OBJECT_NAME = "country_spec".freeze
+    OBJECT_NAME = "country_spec"
   end
 end

lib/stripe/resources/coupon.rb

@@ -7,6 +7,6 @@ class Coupon < APIResource
     extend Stripe::APIOperations::List
     include Stripe::APIOperations::Save
 
-    OBJECT_NAME = "coupon".freeze
+    OBJECT_NAME = "coupon"
   end
 end

lib/stripe/resources/credit_note.rb

@@ -6,7 +6,7 @@ class CreditNote < APIResource
     extend Stripe::APIOperations::List
     include Stripe::APIOperations::Save
 
-    OBJECT_NAME = "credit_note".freeze
+    OBJECT_NAME = "credit_note"
 
     custom_method :void_credit_note, http_verb: :post, http_path: "void"
 

lib/stripe/resources/customer.rb

@@ -8,7 +8,7 @@ class Customer < APIResource
     include Stripe::APIOperations::Save
     extend Stripe::APIOperations::NestedResource
 
-    OBJECT_NAME = "customer".freeze
+    OBJECT_NAME = "customer"
 
     nested_resource_class_methods :balance_transaction,
                                   operations: %i[create retrieve update list]

lib/stripe/resources/customer_balance_transaction.rb

@@ -5,7 +5,7 @@ class CustomerBalanceTransaction < APIResource
     extend Stripe::APIOperations::List
     include Stripe::APIOperations::Save
 
-    OBJECT_NAME = "customer_balance_transaction".freeze
+    OBJECT_NAME = "customer_balance_transaction"
 
     def resource_url
       if !respond_to?(:customer) || customer.nil?

lib/stripe/resources/discount.rb

@@ -2,6 +2,6 @@
 
 module Stripe
   class Discount < StripeObject
-    OBJECT_NAME = "discount".freeze
+    OBJECT_NAME = "discount"
   end
 end

lib/stripe/resources/dispute.rb

@@ -5,7 +5,7 @@ class Dispute < APIResource
     extend Stripe::APIOperations::List
     include Stripe::APIOperations::Save
 
-    OBJECT_NAME = "dispute".freeze
+    OBJECT_NAME = "dispute"
 
     custom_method :close, http_verb: :post
 

lib/stripe/resources/ephemeral_key.rb

@@ -5,7 +5,7 @@ class EphemeralKey < APIResource
     extend Stripe::APIOperations::Create
     include Stripe::APIOperations::Delete
 
-    OBJECT_NAME = "ephemeral_key".freeze
+    OBJECT_NAME = "ephemeral_key"
 
     def self.create(params = {}, opts = {})
       opts = Util.normalize_opts(opts)

lib/stripe/resources/event.rb

@@ -4,6 +4,6 @@ module Stripe
   class Event < APIResource
     extend Stripe::APIOperations::List
 
-    OBJECT_NAME = "event".freeze
+    OBJECT_NAME = "event"
   end
 end

lib/stripe/resources/exchange_rate.rb

@@ -4,6 +4,6 @@ module Stripe
   class ExchangeRate < APIResource
     extend Stripe::APIOperations::List
 
-    OBJECT_NAME = "exchange_rate".freeze
+    OBJECT_NAME = "exchange_rate"
   end
 end

lib/stripe/resources/file.rb

@@ -5,13 +5,13 @@ class File < APIResource
     extend Stripe::APIOperations::Create
     extend Stripe::APIOperations::List
 
-    OBJECT_NAME = "file".freeze
+    OBJECT_NAME = "file"
 
     # This resource can have two different object names. In latter API
     # versions, only `file` is used, but since stripe-ruby may be used with
     # any API version, we need to support deserializing the older
     # `file_upload` object into the same class.
-    OBJECT_NAME_ALT = "file_upload".freeze
+    OBJECT_NAME_ALT = "file_upload"
 
     def self.resource_url
       "/v1/files"

lib/stripe/resources/file_link.rb

@@ -6,6 +6,6 @@ class FileLink < APIResource
     extend Stripe::APIOperations::List
     include Stripe::APIOperations::Save
 
-    OBJECT_NAME = "file_link".freeze
+    OBJECT_NAME = "file_link"
   end
 end

lib/stripe/resources/invoice.rb

@@ -7,7 +7,7 @@ class Invoice < APIResource
     extend Stripe::APIOperations::List
     include Stripe::APIOperations::Save
 
-    OBJECT_NAME = "invoice".freeze
+    OBJECT_NAME = "invoice"
 
     custom_method :finalize_invoice, http_verb: :post, http_path: "finalize"
     custom_method :mark_uncollectible, http_verb: :post

lib/stripe/resources/invoice_item.rb

@@ -7,6 +7,6 @@ class InvoiceItem < APIResource
     extend Stripe::APIOperations::List
     include Stripe::APIOperations::Save
 
-    OBJECT_NAME = "invoiceitem".freeze
+    OBJECT_NAME = "invoiceitem"
   end
 end

lib/stripe/resources/invoice_line_item.rb

@@ -2,6 +2,6 @@
 
 module Stripe
   class InvoiceLineItem < StripeObject
-    OBJECT_NAME = "line_item".freeze
+    OBJECT_NAME = "line_item"
   end
 end

lib/stripe/resources/issuer_fraud_record.rb

@@ -4,6 +4,6 @@ module Stripe
   class IssuerFraudRecord < APIResource
     extend Stripe::APIOperations::List
 
-    OBJECT_NAME = "issuer_fraud_record".freeze
+    OBJECT_NAME = "issuer_fraud_record"
   end
 end

lib/stripe/resources/issuing/authorization.rb

@@ -6,7 +6,7 @@ class Authorization < APIResource
       extend Stripe::APIOperations::List
       include Stripe::APIOperations::Save
 
-      OBJECT_NAME = "issuing.authorization".freeze
+      OBJECT_NAME = "issuing.authorization"
 
       custom_method :approve, http_verb: :post
       custom_method :decline, http_verb: :post

lib/stripe/resources/issuing/card.rb

@@ -7,7 +7,7 @@ class Card < APIResource
       extend Stripe::APIOperations::List
       include Stripe::APIOperations::Save
 
-      OBJECT_NAME = "issuing.card".freeze
+      OBJECT_NAME = "issuing.card"
 
       custom_method :details, http_verb: :get
 

lib/stripe/resources/issuing/card_details.rb

@@ -3,7 +3,7 @@
 module Stripe
   module Issuing
     class CardDetails < Stripe::StripeObject
-      OBJECT_NAME = "issuing.card_details".freeze
+      OBJECT_NAME = "issuing.card_details"
     end
   end
 end

lib/stripe/resources/issuing/cardholder.rb

@@ -7,7 +7,7 @@ class Cardholder < APIResource
       extend Stripe::APIOperations::List
       include Stripe::APIOperations::Save
 
-      OBJECT_NAME = "issuing.cardholder".freeze
+      OBJECT_NAME = "issuing.cardholder"
     end
   end
 end

lib/stripe/resources/issuing/dispute.rb

@@ -7,7 +7,7 @@ class Dispute < APIResource
       extend Stripe::APIOperations::List
       include Stripe::APIOperations::Save
 
-      OBJECT_NAME = "issuing.dispute".freeze
+      OBJECT_NAME = "issuing.dispute"
     end
   end
 end