Nav fixes

Hey Eddie,

I'm not sure about either of the commits in this pull request, so junk it if I've misunderstood.

I just started a project based on bones and ran across what seemed like some typos in the less and sass for the .nav + .menu elements.

Then when digging through some other nav-related stuff in bones.php I noticed what I thought was a typo in the nav classes for the main-nav fallback function.