Add support for intridea/grape

batch_api currently does not play well with
grape APIs (intridea/grape) on various parameter passing issues.
This pull request helps to let them work together.
Use Ruby 2.x in lieu of the out-dated Ruby 1.9

* Update travis config
* Use pry since debugger is no longer supported for Ruby 2.1
* Use better group syntax in Gemfile
Merge branch 'supporting_grape'