Add ruby 2.1.1 to Travis
Delete ruby 1.8.7, 1.9.2 and 1.9.3 from Travis
Delete .ruby-version
Add jruby-head-d20 and jruby-head-d21 to Travis
Delete jruby-18mode and jruby-19mode from Travis
Delete ree from Travis
Delete rbx-18mode and rbx-19mode from Travis
Update development dependencies