Add `sans-serif` fallback

[Dandandan]

On linux there is no Tahoma font, so the menu bar looks weird with a serif font. Adding sans-serif as fallback looks much better.

.litemenubar ul {
    font-family: Tahoma, sans-serif;
    margin: 0;
    padding: 0;
}

Before:

After:

[jagenjo]

Fixed, thanks a lot for the tip. Btw, you are my first comment in github, I owe you a beer!

[Dandandan]

Haha cool!