fixed js

js/nav-tabs.es6.js

@@ -9,7 +9,9 @@
     const $tab = $(tab);
     const $target = $tab.find('[data-drupal-nav-tabs-target]');
 
-    const openMenu = () => {
+    const openMenu = event => {
+      event.preventDefault();
+
       $target.toggleClass('is-open');
       const $toggle = $target.find('.tab-toggle');
       $toggle.attr(

js/nav-tabs.js

@@ -10,7 +10,9 @@
     var $tab = $(tab);
     var $target = $tab.find('[data-drupal-nav-tabs-target]');
 
-    var openMenu = function openMenu() {
+    var openMenu = function openMenu(event) {
+      event.preventDefault();
+
       $target.toggleClass('is-open');
       var $toggle = $target.find('.tab-toggle');
       $toggle.attr('aria-expanded', function (_, isExpanded) {