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`
Can you use default parameter? It reduces conditional expression by Rails version.

```ruby
# Rails 4.2 above will not pass `error`.
def api_behavior(error = nil)
```