switch to async widget.js script

Author: fat

docs/index.html

@@ -112,7 +112,7 @@ <h3>History</h3>
       <p>Read more on <a href="https://dev.twitter.com/blog/bootstrap-twitter">dev.twitter.com &rsaquo;</a></p>
       <p>
         <a href="http://twitter.com/twbootstrap" class="twitter-follow-button">Follow @twbootstrap</a>
-        <script src="http://platform.twitter.com/widgets.js" type="text/javascript"></script>
+        <script>!function(d,s,id){var js,fjs=d.getElementsByTagName(s)[0];if(!d.getElementById(id)){js=d.createElement(s);js.id=id;js.src="//platform.twitter.com/widgets.js";fjs.parentNode.insertBefore(js,fjs);}}(document,"script","twitter-wjs");</script>
       </p>
     </div>
     <div class="span-one-third">