Specify jRuby version on Travis CI
Specify jRuby version on Travis CI

To fix the followring error:
> $ rvm use jruby --install --binary --fuzzy
> Unknown ruby string (do not know how to handle): jruby-9.1.15.0200.

https://travis-ci.org/tchak/barber/jobs/326895117

tchak/barber,tchak/barber