Create .travis.yml

This package is perfect for CI and it has no dependencies so the feedback is instantaneous. All you need to do is activate this repo from <http://travis-ci.org/>.

It would also be nice to have a status image like here: <https://github.com/Tarrasch/vault/tree/9881215fbf80699f19f768bd0fb2760cc8527bcc>

I think CI for this project is motivated as of the recent build troubles involving this package.