Use cdn.polyfill.io for polyfills

config/examples/strapless.html

@@ -11,6 +11,7 @@
     <link rel="stylesheet" href="./resources/layout.css" type="text/css">
     {{{ extraHead.local }}}
     {{{ css.tag }}}
+    <script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=fetch"></script>
     <script src="./resources/zeroclipboard/ZeroClipboard.min.js"></script>
     <title>{{ title }}</title>
   </head>