upgrade to CE v7.5.1 and shell v2.2.0

Upgraded the repo to the newest version of GitLab (7.5.1) and GitLab Shell (2.2.0). Tested the Dockerfile and successfully built the image and booted up.

![screen shot 2014-11-22 at 5 24 02 pm](https://cloud.githubusercontent.com/assets/449321/5156047/7e273cd6-726c-11e4-88c2-6ffe93724ece.png)