Drop old rails support

.travis.yml

@@ -15,13 +15,14 @@ env:
   - RAILS=v5.2.0 DB=mysql
   - RAILS=v5.2.0 DB=postgres
 
+  - RAILS=5-1-stable DB=sqlite3
+  - RAILS=5-1-stable DB=mysql
+  - RAILS=5-1-stable DB=postgres
+
   - RAILS=5-0-stable DB=sqlite3
   - RAILS=5-0-stable DB=mysql
   - RAILS=5-0-stable DB=postgres
 
-  - RAILS=4-2-stable DB=sqlite3
-  - RAILS=4-2-stable DB=mysql
-  - RAILS=4-2-stable DB=postgres
 matrix:
   allow_failures:
     - env: RAILS=5-2-stable DB=sqlite3

lib/polyamorous.rb

@@ -24,28 +24,15 @@ module Polyamorous
   require 'polyamorous/swapping_reflection_class'
 
   ar_version = ::ActiveRecord::VERSION::STRING[0,3]
-  ar_version = '3_and_4.0' if ar_version < '4.1'
   ar_version = ::ActiveRecord::VERSION::STRING[0,5] if ar_version == '5.2'
 
-  method, ruby_version =
-    if RUBY_VERSION >= '2.0' && ar_version >= '4.1'
-      # Ruby 2; we can use `prepend` to patch Active Record cleanly.
-      [:prepend, '2']
-    else
-      # Ruby 1.9; we must use `alias_method` to patch Active Record.
-      [:include, '1.9']
-    end
-
   %w(join_association join_dependency).each do |file|
-    require "polyamorous/activerecord_#{ar_version}_ruby_#{ruby_version}/#{file}"
+    require "polyamorous/activerecord_#{ar_version}_ruby_2/#{file}"
   end
 
-  Polyamorous::JoinDependency.send(method, Polyamorous::JoinDependencyExtensions)
-  if method == :prepend
-    Polyamorous::JoinDependency.singleton_class
-    .send(:prepend, Polyamorous::JoinDependencyExtensions::ClassMethods)
-  end
-  Polyamorous::JoinAssociation.send(method, Polyamorous::JoinAssociationExtensions)
+  Polyamorous::JoinDependency.send(:prepend, Polyamorous::JoinDependencyExtensions)
+  Polyamorous::JoinDependency.singleton_class.send(:prepend, Polyamorous::JoinDependencyExtensions::ClassMethods)
+  Polyamorous::JoinAssociation.send(:prepend, Polyamorous::JoinAssociationExtensions)
 
   Polyamorous::JoinBase.class_eval do
     if method_defined?(:active_record)