Prevent nav menu from remaining hidden

The the script that toggles the nav menu in the mobile-style layout hides it with a `display: none;`. If the viewport is then increased to be >= 768px, it will switch to the desktop-style layout, however the menu remains hidden due to the `display: none;`.

![Vagrant_Nav_Issue](https://f.cloud.github.com/assets/84348/266367/be36d64e-8df1-11e2-9776-b051d7026b3a.png)