Add some flexy to the picks container

Sexy flexy.
See for yourself:

### Desktop
![desktop](https://cloud.githubusercontent.com/assets/31692/3935071/b8c8e084-2491-11e4-9f01-affd2cf57633.png)

### Tablet
![tablet](https://cloud.githubusercontent.com/assets/31692/3935073/b8daa4a4-2491-11e4-8eaf-976de92ecdb6.png)

### Mobile
![mobile](https://cloud.githubusercontent.com/assets/31692/3935072/b8da3f64-2491-11e4-8e23-9d98cdb99ba0.png)

### Desktop (no flex)
![desktop-noflex](https://cloud.githubusercontent.com/assets/31692/3935070/b8b52eb8-2491-11e4-9517-a32a39d0037b.png)

### Tablet (no flex)
![tablet-noflex](https://cloud.githubusercontent.com/assets/31692/3935074/b8e39ab4-2491-11e4-9b7d-c6a7fd818802.png)
https://github.com/guardian/guss-css3/pull/5