Travis

* Build with MRI 1.8.7, 1.9.2, and 1.9.3 on Travis


* Add Travis badge


Build is green: http://travis-ci.org/#!/joliss/hub
Don't forget to enable the build on http://travis-ci.org/profile

I wanted to tie down 1.8.7 compatibility with this. It's important for me for performance reasons, as Ruby 1.8.7 (as installed by apt-get) has the lowest startup time on my system.