Remove es6-promise script, simply point to repo

Author: danielstjules

README.md

@@ -251,10 +251,6 @@ storage.onConnect().then(function() {
 For compatibility with older browsers, simply load a Promise polyfill such as
 [es6-promise](https://github.com/jakearchibald/es6-promise).
 
-``` html
-<script src="https://s3.amazonaws.com/es6-promises/promise-1.0.0.min.js"></script>
-```
-
 You can also use RSVP or any other ES6 compliant promise library. Supports IE8
 and up using the above polyfill. A JSON polyfill is also required
 for IE8 in Compatibility View. Also note that `catch` is a reserved word in IE8,