enable travis-ci builds

This enables travis-ci builds.

Once you merge this pull request, all you have to do is login on https://travis-ci.org and flip a switch. It literally takes __less than 1 minute__.

If you don't already know travis-ci, it is a service that pulls every commit launches builds.

- You can take a look at my shinken build examples here: https://travis-ci.org/ReAzem/shinken/builds
- This is what a pull request will look like when travis-ci is enabled: https://github.com/ReAzem/shinken/pull/1