Adding Ruby parser

Hi guys,

Thanks for the inspiring and useful project! Learning babel transformations with it is a pure joy 👍

Are you interested in adding a Ruby parser? I've developed [ruby-parser.js](https://github.com/peter-leonov/ruby-parser.js) ([live demo](http://peter-leonov.github.io/ruby-parser.js/)) for fun in pure JavaScript. It can also be of use to someone learning Ruby. I'm fine with making a PR if you find it interesting.