.navmenu height fix

The `.navmenu` height needs to be set to `auto` in order to allow the `top` and `bottom` values to properly work. The `top` value works fine, but the `bottom` value is rendered inert because the `height: 100%` causes the `.navmenu` to overflow down through the viewport.
Merge pull request #239 from phaseOne/patch-2

.navmenu height fix