Update polyfill URL (#225)

Update polyfill URL from v2 to v3

index.html

@@ -279,7 +279,7 @@ <h1>Download</h1>
 	<script>!function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0],p=/^http:/.test(d.location)?'http':'https';if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src=p+'://platform.twitter.com/widgets.js';fjs.parentNode.insertBefore(js,fjs);}}(document, 'script', 'twitter-wjs');</script>
 </footer>
 
-<script src="https://cdn.polyfill.io/v2/polyfill.min.js?features=blissfuljs"></script>
+<script src="https://polyfill.io/v3/polyfill.min.js?features=blissfuljs"></script>
 <script src="bliss.js"></script>
 <script src="transform.js"></script>
 <script src="index.js"></script>