fixes undefined local variable or method attributes_names

I set in rails_app/config/application.rb,

    config.generators.template_engine :jbuilder

and run command.

    rails g scaffold Post title body:text

I found a error.

    jbuilder_generator.rb:35:in `attributes_list': undefined local variable or method `attributes_names'

Rails version is 3.2.13 and ruby is 1.9.3.

This codes maybe fix it, but I don't know how to test generators.