Improve Travis-CI Badge Rendering in Docs

* destretch by removing dimensions, also future proofs size changes
* forcibly move to next line
* uses css attr selector, other strategies may be better

![Screen Shot 2013-02-26 at 8 26 16 PM](https://f.cloud.github.com/assets/3456/199473/718a3044-8085-11e2-8467-23f733e02e1e.png)