Bumps ruby to 2.1.2

* Removes pry-debugger in favour of ruby 2.1.2 compatible version
* Adds .ruby-version file for determining ruby version locally
* Adds ruby configuration to the Gemfile for heroku
* Updates travis-ci configuration to build/test with 2.1.2

I'm gonna be picking off a bunch of issues but wanted to get things updated first :heart: