Don't use polyfill.io unless necessary

_includes/polyfills.html

@@ -1,4 +1,5 @@
-<script src='https://cdn.polyfill.io/v2/polyfill.min.js'></script>
+<script>(function(d,s){if(window.Promise&&[].includes&&Object.assign&&window.Map)return;var js,sc=d.getElementsByTagName(s)[0];js=d.createElement(s);js.src='https://cdn.polyfill.io/v2/polyfill.min.js';sc.parentNode.insertBefore(js, sc);}(document,'script'))</script>
+
 <!--[if lt IE 9]>{%comment%}
 {%endcomment%}<script src='//cdnjs.cloudflare.com/ajax/libs/nwmatcher/1.2.5/nwmatcher.min.js'></script>{%comment%}
 {%endcomment%}<script src='//cdnjs.cloudflare.com/ajax/libs/json2/20140204/json2.js'></script>{%comment%}