Adding travis support

Unless there is a explict reason you are not using Travis I thought it would be a useful addition as an opensource CI tool.

https://travis-ci.org/

I've added the pre-requisite files. 
You would need to create a travis account and connect Midje.

I also added the travis current build status to the readme (see as an example: https://github.com/josephwilk/stereotype-clj)