Use modern flexbox syntax

Fixes display issues with Firefox

Resolve #65

## Before

![screen shot 2014-04-28 at 2 54 27 pm](https://cloud.githubusercontent.com/assets/407342/2823489/bf965116-cf1f-11e3-92c8-b9e7bbf0546d.png)

## After

![screen shot 2014-04-28 at 2 54 39 pm](https://cloud.githubusercontent.com/assets/407342/2823490/c33fe502-cf1f-11e3-9ed2-5dc84d22a0ae.png)