Prevent images with another ratio than 5/3 to break out of their container

Outbrain seems to return square images. This fixes the case where it was interfering with the layout. 

## Before

![screen shot 2014-02-23 at 14 10 53](https://f.cloud.github.com/assets/85783/2240475/937627e0-9c94-11e3-97a9-0a4093579af1.PNG)


## After

![screen shot 2014-02-23 at 14 10 49](https://f.cloud.github.com/assets/85783/2240476/9683ca5a-9c94-11e3-941b-7a681597868f.PNG)


![ ](http://media.giphy.com/media/13y1jWA5jbaW7C/giphy.gif)