Avoid hotlinking twitter resources

No idea what happened, but it seems that replacing the weird black magic that creates a script element to load twitter js with a reveal-md script works, better. The first slide is no longer emptied.

embed-tweet.js

 var RevealEmbedTweet = window.RevealEmbedTweet || (function(){
 	var ready = false;
-	window.twttr = (function(d, s, id) {
-		var js, fjs = d.getElementsByTagName(s)[0],
-				t = window.twttr || {};
-		if (d.getElementById(id)) return t;
-		js = d.createElement(s);
-		js.id = id;
-		js.src = "https://platform.twitter.com/widgets.js";
-		fjs.parentNode.insertBefore(js, fjs);
-
-		t._e = [];
-		t.ready = function(f) {
-				t._e.push(f);
-		};
-	}(document, "script", "twitter-wjs"));
-
 
 	function load() {
-		if ( twttr != undefined && !document.querySelector('section[data-markdown]:not([data-markdown-parsed])') ) {
+		if ( window.twttr != undefined && !document.querySelector('section[data-markdown]:not([data-markdown-parsed])') ) {
 			tweets = document.querySelectorAll(".tweet");
 			for (i = 0; i < tweets.length; ++i) {
 				tweets[i].style.cssText = "margin: 0;position: absolute; left: 50%;transform: translate(-50%,0%);" + tweets[i].style.cssText;
 				tweets[i].innerHTML = 	'<blockquote class="twitter-tweet" data-lang="en"><a href="' + tweets[i].getAttribute('data-src') + '">Tweet</a></blockquote>';
 			}
-			twttr.widgets.load()
+			window.twttr.widgets.load()
 		}
 		else {
 			// wait for markdown to be loaded and parsed