Update wercker-box.yml

Inherit from the `wercker/ubuntu12.04-nodejs0.10@0.0.1` box and only install af gem in provision script.
Merge pull request #1 from pjvds/master

Update wercker-box.yml
Inherit from the wercker/ubuntu12.04-nodejs0.10@0.0.1 box and only install af gem in provision script.