Use ActiveSupport.on_load to correctly re-open ActiveRecord::Base.…

Use ActiveSupport.on_load to correctly re-open ActiveRecord::Base. https://github.com/rubysherpas/paranoia/issues/335

lib/paranoia.rb

@@ -205,7 +205,8 @@ module Paranoia
   end
 end
 
-class ActiveRecord::Base
+ActiveSupport.on_load(:active_record) do
+  class ActiveRecord::Base
     def self.acts_as_paranoid(options={})
       alias_method :really_destroyed?, :destroyed?
       alias_method :really_delete, :delete
@@ -256,6 +257,7 @@ class ActiveRecord::Base
     def paranoia_sentinel_value
       self.class.paranoia_sentinel_value
     end
+  end
 end
 
 require 'paranoia/rspec' if defined? RSpec