Support Rails4.2

Hi!
I want to use this product in a Rails 4.2 application, so I've just implemented.

For Rails 4.2 supports,
- `require 'action_controller/responder'` #2 
- no arguments for `Garage::OptionalResponseBodyResponder#api_behavior`
Oh, that's right.

When you branch by Rails version, please use `Rails::VERSION::{MAJOR,MINOT,TINY,PRE}` constants or `gem_version`.