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
Merge pull request #123 from 1minus1limited/master

Bumps ruby to 2.1.2