TST add travis support

Adds travis support see: http://about.travis-ci.org/docs/user/getting-started/

Unfortunately at the moment there are 16 test failures in mocha, which I see on my local system too (perhaps I've not installed something correctly?)... See this failure report: https://travis-ci.org/hayd/emblem.js/jobs/10318315.

*Thanks for the gem!*