fix(menu): Fix menu demo after component namespacing.

Author: Sérgio Gomes

demos/simple-menu.html

@@ -73,7 +73,7 @@ <h1>MDL Simple Menu</h1>
 
     <script src="../assets/material-design-lite.js" charset="utf-8"></script>
     <script>
-      var menu = new mdl.SimpleMenu(document.querySelector('.mdl-simple-menu'));
+      var menu = new mdl.menu.MDLSimpleMenu(document.querySelector('.mdl-simple-menu'));
       document.querySelector('.toggle').addEventListener('click', function() {
         menu.open = !menu.open;
       });