Add word-wrap to contribute cards

Before:
![image](https://f.cloud.github.com/assets/2641501/1460787/c07af86e-4470-11e3-8a28-a654579e5435.png)


After:
![image](https://f.cloud.github.com/assets/2641501/1460786/bc44a790-4470-11e3-86b8-778e576b69d9.png)

This change is especially important for the mobile site.