Fix #164: Remove hard-coded height for horizontal menus

I removed the hard-coded height. The `<ul>` now has `height: auto` by default.

#### This has been tested on:

* iOS7
* Latest Chrome/FF
* Safari 6 (I don't have Mavericks though)
* IE7+

I haven't tested this on Android, but it's a height fix, so I think it'll be ok. If someone would like to test it for me, just open the menu manual test page and take a look at the second menu (the blue one).