Avoid loading ActionController::API constant

Copies rails/jbuilder#529

Author: ghiculescu

lib/rabl/railtie.rb

@@ -10,11 +10,9 @@ module ApiRendering
           end
         end
 
-        ActiveSupport.on_load :action_controller do
-          if self == ActionController::API
-            include ActionController::Helpers
-            include ActionController::ImplicitRender
-          end
+        ActiveSupport.on_load :action_controller_api do
+          include ActionController::Helpers
+          include ActionController::ImplicitRender
         end
       end