Sponsored containers' headers need min-width

### Before

![screen shot 2014-10-23 at 11 18 21](https://cloud.githubusercontent.com/assets/74132/4751420/f06f8622-5a9d-11e4-8e23-eef4828e9f47.png)

### After

![screen shot 2014-10-23 at 11 18 25](https://cloud.githubusercontent.com/assets/74132/4751421/f248b2de-5a9d-11e4-9e96-a28e2319a66f.png)