Ensure taps aren't accidentally sent to the modal

Without stopping the propagation of the event which pops up the modal,
it was possible for the modal itself to receive the same event.

lib/js/modals.js

@@ -19,7 +19,8 @@
   };
 
   window.addEventListener('touchend', function (event) {
+    event.stopPropagation();
     var modal = getModal(event);
     if (modal) modal.classList.toggle('active');
   });
-}();
+}();