Fixed main menu @ Redmine 2.3.0 stable

Hi, I've just installed your gitlab theme @ Redmine 2.3.0-stable and I've found a problem of the position of main menu.

![before](https://f.cloud.github.com/assets/212607/371126/6d75a4a4-a31a-11e2-951e-8a18c26d8e11.png)

I've fixed this problem and here is the result.

![after](https://f.cloud.github.com/assets/212607/371127/929bb642-a31a-11e2-8eda-4fc03c717328.png)

Could you please merge this ?