rvm:
  - 1.8.7
  - 1.9.1
  - 1.9.2
  - jruby
  - rbx
  - ree

rvm:
  - 1.8.7
  - 1.9.2
  - jruby
  - rbx
  - ree
  - ruby-head

Test ruby-head instead of 1.9.1
Test ruby-head instead of 1.9.1

Bundler seems to have dropped support for Ruby 1.9.1. So we start to test
against ruby-head, that's the future.