ORM agnosticism: do not `require activerecord`, and instead only load the ransack AR adapters if AR has already been defined

Fixes #296

lib/ransack.rb

@@ -19,7 +19,7 @@ end
 require 'ransack/translate'
 require 'ransack/search'
 require 'ransack/ransacker'
-require 'ransack/adapters/active_record'
+require 'ransack/adapters/active_record' if defined?(::ActiveRecord::Base)
 require 'ransack/helpers'
 require 'action_controller'
 

lib/ransack/adapters/active_record.rb

@@ -1,4 +1,3 @@
-require 'active_record'
 require 'ransack/adapters/active_record/base'
 ActiveRecord::Base.extend Ransack::Adapters::ActiveRecord::Base