Hide teams section when members list is empty

Pretty hacky fix for GH-414, there is likely to be better ways to do this but my jekyll-fu is kinda limited at the moment.

As discussed on that issue, ideally we should show up the team member picture even for those who have left the company but I can't think of an easy way of doing that.

#### With no team members

![image](https://cloud.githubusercontent.com/assets/81859/3559091/f639fb1e-0944-11e4-8723-08c706e1634f.png)

#### With team members

![image](https://cloud.githubusercontent.com/assets/81859/3559098/155bdfd0-0945-11e4-9739-c59c7ad2efb3.png)