diff --git a/.tool-versions b/.tool-versions
new file mode 100644
index 00000000..9b6768d1
--- /dev/null
+++ b/.tool-versions
@@ -0,0 +1 @@
+ruby 2.6.7
diff --git a/Gemfile b/Gemfile
index 184fe0ba..4acd9cb8 100644
--- a/Gemfile
+++ b/Gemfile
@@ -1,6 +1,6 @@
 source 'https://rubygems.org'
 
-ruby '>= 2.2.0'
+ruby '>= 2.4.0'
 
 gem 'activerecord', '>= 4.2.5', '< 6', require: false
 gem 'rake', require: false
@@ -20,7 +20,10 @@ group :development, :test do
   gem 'rspec', require: false
 
   gem 'rubocop', '~> 0.68.1', require: false unless RUBY_VERSION =~ /^1.8/
-  gem 'simplecov', require: false
+  # gem 'rubocop', '~> 1.12', require: false
+  # gem 'rubocop-rake', require: false
+  # gem 'rubocop-rspec', require: false
+  # gem 'simplecov', require: false
   gem 'terminal-notifier-guard', require: false
 
   gem 'codeclimate-test-reporter'
diff --git a/Guardfile b/Guardfile
index 602c7b57..f93bc135 100644
--- a/Guardfile
+++ b/Guardfile
@@ -1,4 +1,4 @@
-# Note: The cmd option is now required due to the increasing number of ways
+# NOTE: The cmd option is now required due to the increasing number of ways
 #       rspec may be run, below are examples of the most common uses.
 #  * bundler: 'bundle exec rspec'
 #  * bundler binstubs: 'bin/rspec'
diff --git a/Rakefile b/Rakefile
index bfbd51b7..43944f2d 100644
--- a/Rakefile
+++ b/Rakefile
@@ -3,7 +3,7 @@ def exit_exception(e)
   exit e.status_code
 end
 
-# Note : this causes annoying psych warnings under Ruby 1.9.2-p180; to fix, upgrade to 1.9.3
+# NOTE: this causes annoying psych warnings under Ruby 1.9.2-p180; to fix, upgrade to 1.9.3
 begin
   require 'bundler'
   Bundler.setup(:default, :development)
@@ -162,7 +162,7 @@ namespace :integration do
       fixtures[Digest::MD5.hexdigest(File.read(fname))] = File.expand_path(fname)
     end
 
-    candidates.keys.each do |digest|
+    candidates.each_key do |digest|
       next unless fixtures.key?(digest)
       candidates[digest].each do |fname|
         # Double-check contents in case of hash collision...