Introduce .is-active to the active nav class as used from Foundation …

…6.4.0 onwards

This addresses issues found in #397 where the $dropdown-menu-item-background-active didn't seem to apply. But the actual issue is Foundation now uses .is-active and not .active.

To preserve back-compat for other devs I've left .active present.

functions/menu.php

@@ -85,7 +85,8 @@ function joints_footer_links_fallback() {
 function required_active_nav_class( $classes, $item ) {
  if ( $item->current == 1 || $item->current_item_ancestor == true ) {
  $classes[] = 'active';
+ $classes[] = 'is-active';
  }
  return $classes;
 }
-add_filter( 'nav_menu_css_class', 'required_active_nav_class', 10, 2 );
+add_filter( 'nav_menu_css_class', 'required_active_nav_class', 10, 2 );