Correctly size rating widget stars (bug 1057283)

r? @spasovski @ngokevin

## Before

![screen shot 2014-08-22 at 9 57 19 am](https://cloud.githubusercontent.com/assets/23885/4013299/0e5fbad0-2a15-11e4-9228-7f9d9f1a23fe.png)

## After

![screen shot 2014-08-22 at 9 56 38 am](https://cloud.githubusercontent.com/assets/23885/4013302/1616ebcc-2a15-11e4-8a2f-9c2404c6c4b4.png)