Fix cutouts inside item--third

The cutouts on `item--third`s weren't playing so nicely. This sorts them out across the breakpoints.

Before:
![screen shot 2014-11-26 at 15 09 27](https://cloud.githubusercontent.com/assets/1607666/5203475/e03cddf8-757e-11e4-9741-1beaf950fe69.png)

After:
![screen shot 2014-11-26 at 15 09 12](https://cloud.githubusercontent.com/assets/1607666/5203478/e3a70cb6-757e-11e4-91e0-7771f14e1717.png)