correction to javascript code sample

index.html

@@ -231,7 +231,7 @@
 					<p>
 						Additionally custom events can be triggered on a per slide basis by binding to the <code>data-state</code> name.
 					</p>
-					<pre><code data-trim contenteditable style="font-size: 18px; margin-top: 20px;">
+					<pre><code class="javascript" data-trim contenteditable style="font-size: 18px;">
 Reveal.addEventListener( 'customevent', function() {
 	console.log( '"customevent" has fired' );
 } );