stop using underscore.org

tests/frontend/index.html

@@ -10,7 +10,7 @@
     <div id="iframe-container"></div>
 
     <script src="/static/js/jquery.js"></script>
-    <script src="http://underscorejs.org/underscore.js"></script>
+    <script src="lib/underscore.js"></script>
 
     <script src="lib/mocha.js"></script>
     <script> mocha.setup('bdd') </script>