Fix sort dropdown partially not showing on screen.

This MR fixes the sort dropdown menu partially not showing on the screen.
Closes gitlab-org/gitlab-ce#986

Screenshot of the Problem:
![Problem](https://gitlab.com/uploads/gitlab-org/gitlab-ce/8d442e872c/Screenshot_from_2015-01-17_15_18_41.png)

@dzaporozhets Can you take a look at this?

See merge request !299