Fix aspect ratio problem of the cover (Detailview)

This PR fixes the aspect ratio problem on resize in the detailview.

After:
![2014-09-01](https://cloud.githubusercontent.com/assets/5322473/4109186/fea62686-31e1-11e4-9fab-7782c119506a.png)

Before:
![2014-08-29](https://cloud.githubusercontent.com/assets/5322473/4109188/010dccc6-31e2-11e4-9876-45f1df5ac1ad.png)