Update _768up.less

I was working with bones and found a small error under navigation, 'li.current-page-ancestor' should be 'li.current_page_ancestor' (2 occurrences).

I am new to programming, learning to make wordpress themes. :)
Fix accessibility issue in the menu and cleaned up some CSS.
fix classname li.current_page_ancestor

It was li.current-page-ancestor before. wordpress uses li.current_page_ancestor
Minor Inconsitency
Merge pull request #515 from blowsie/patch-6

Minor Inconsitency
Merge pull request #500 from elron/patch-21

fix classname li.current_page_ancestor
Merge pull request #491 from bgallagh3r/master

Fix accessibility issue in the menu and cleaned up some CSS.
Merge pull request #415 from gthapar/patch-1

Update _768up.less
Merge pull request #1 from eddiemachado/master

merge updates