Update .travis.yml

  * Always specify the language
  * Test against ruby-2.2.0-preview1, jruby-head and rbx 2.4.1
  * Allow jruby-head and rbx-2.4.1 to fail
Rubinius support!
Replace an if statement with when/case
Extract format method into a separate class
Add Pry formatter
Remove methods that haven't been used
:point_right: :point_right: :point_right: