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. :)

library/less/_768up.less

@@ -110,7 +110,7 @@ NAVIGATION STYLES
 			/* highlight sub-menu current page */
 			li.current-menu-item,
 			li.current_page_item,
-			li.current-page-ancestor {
+			li.current_page_ancestor {
 				a {}
 			}
 		}
@@ -126,7 +126,7 @@ NAVIGATION STYLES
 	/* highlight current page */
 	li.current-menu-item,
 	li.current_page_item,
-	li.current-page-ancestor {
+	li.current_page_ancestor {
 		a {}
 	}  /* end current highlighters */