enable docker builds

### What is the problem / feature ?

Docker builds are avaliable and not being used

### How did it get fixed / implemented ?

set `sudo: false` in `.travis.yml` to enable docker builds.

### How can someone test / see it ?

See builds are faster.

*Here is a cute animal picture for your troubles...*

![209581-socks-the-shetland-pony-in-christmas-advert-for-visitscotlnad](https://cloud.githubusercontent.com/assets/824194/5507859/6309d82a-8764-11e4-8e23-f4c226bb6ce0.jpg)