Fix React example

examples/timeline/other/usingReact.html

@@ -93,7 +93,7 @@
                 return ReactDOM.render(<ItemTemplate item={item} />, element);
             },
             groupTemplate: function (group, element) {
-                if (!item) { return }
+                if (!group) { return }
                 ReactDOM.unmountComponentAtNode(element);
                 return ReactDOM.render(<GroupTemplate group={group} />, element);
             }