Add missing dependency

### What is the problem / feature ?

The tests were failing because `factoryboy` wasn't installed.

### How did it get fixed / implemented ?

Added it to `requirements.txt`

### How can someone test / see it ?

See that the travis tests pass

*Here is a cute baby animal picture for your troubles...*

![cat_bunny3-1](https://f.cloud.github.com/assets/824194/2368412/72b8a7f8-a7a7-11e3-8f1b-68c177119c59.jpg)