Use ActiveSupport.on_load to extend ActionController and ActionView.

http://api.rubyonrails.org/classes/ActiveSupport/LazyLoadHooks.html
https://github.com/rails/rails/blob/92703a9ea5d8b96f30e0b706b801c9185ef14f0e/actionpack/lib/action_controller/base.rb#L264
https://github.com/rails/rails/blob/7da8d76206271bdf200ea201f7e5a49afb9bc9e7/actionview/lib/action_view/base.rb#L215

lib/rucaptcha.rb

@@ -35,5 +35,10 @@ module RuCaptcha
   end
 end
 
-ActionController::Base.send(:include, RuCaptcha::ControllerHelpers)
-ActionView::Base.send(:include, RuCaptcha::ViewHelpers)
+ActiveSupport.on_load(:action_controller) do
+  ActionController::Base.send :include, RuCaptcha::ControllerHelpers
+end
+
+ActiveSupport.on_load(:active_view) do
+  include RuCaptcha::ViewHelpers
+end