Add to Travis-CI

I noticed that the ruby gem is on travis, but this is not. Ideally, it'd be great to have https://travis-ci.org/SquareSquash/web check on PR statuses. I'd like to add some tests for testing WAR building (as part of #57) so having it run in JRuby as well as MRI (and maybe Rubinius, etc) would be great.

I'm happy to add a `.travis.yml` file if you don't have one you already use.