Migrated .rvmrc to the more modern .ruby-version and ruby-gemset [ci skip]
Just a general jruby instead of jruby-1.7.3 in .ruby-version

* After feedback of @mpapis just chose the general jruby,
  however this doesnt force 1.7+ - solutions welcome!
Merge pull request #242 from PragTob/ruby-version

Migrated .rvmrc to the more modern .ruby-version and ruby-gemset