Update library/less/_base.less

Replaced hyphens with underscores for li.current-page-ancestor to support the fallback menus. li.current-page-ancestor is only used on custom navigation menus (Wordpress 3.4.2).

library/less/_base.less

@@ -248,7 +248,7 @@ and more scalable.
 	/* highlight current page */
 	li.current-menu-item,
 	li.current_page_item,
-	li.current-page-ancestor {
+	li.current_page_ancestor {
 
 		a {}