Fix: Update item count ARIA for grouped items (fixes #160) (#162)

* Update item count for grouped items

* remove _nthChild from updated item count

* set models.length to a variable

Co-authored-by: Brad Simpson <brad.simpson@kineo.com>

* Update js/BoxMenuGroupView.js

---------

Co-authored-by: Brad Simpson <brad.simpson@kineo.com>
Co-authored-by: Oliver Foster <oliver.foster@kineo.com>

js/BoxMenuGroupView.js

@@ -11,6 +11,13 @@ class BoxMenuGroupView extends MenuItemView {
     _.defer(this.addChildren.bind(this));
     this.$el.imageready(this.setReadyStatus.bind(this));
     this.$el.parents('.boxmenu__item-container').addClass('has-groups');
+    this.updateItemCount();
+  }
+
+  updateItemCount() {
+    const models = this.model.getChildren().models;
+    const totalChildren = models.length;
+    models.forEach(model => model.set('_totalChild', totalChildren));
   }
 }