shift down install btn on mobile listing

Install button a bit too close when the content ratings line is at its longest on mobile.

### After

![screen shot 2013-12-06 at 4 25 27 pm](https://f.cloud.github.com/assets/674727/1697223/96f76a9c-5ed6-11e3-812a-f1427e9b5e5c.png)

### Before

![screen shot 2013-12-06 at 4 26 18 pm](https://f.cloud.github.com/assets/674727/1697224/99204d2a-5ed6-11e3-8c73-9cb99e1b83a8.png)