Add combined_fragment_cache_key

Author: excid3

Diff for: lib/jbuilder/railtie.rb

@@ -20,6 +20,7 @@ module ApiRendering
           if name == 'ActionController::API'
             include ActionController::Helpers
             include ActionController::ImplicitRender
+            helper_method :combined_fragment_cache_key
             helper_method :view_cache_dependencies
           end
         end