fix exception in layout examle

examples/layout-helpers.html

@@ -48,9 +48,9 @@
 					<p>Stacks multiple elements on top of each other, for use with fragments.</p>
 					<pre><code class="html" data-trim data-line-numbers>
 					  <div class="r-stack">
-					    <img class="fragment" width="450" height="300" src="...">
-					    <img class="fragment" width="300" height="450" src="...">
-					    <img class="fragment" width="400" height="400" src="...">
+					    &gt;img class="fragment" width="450" height="300" src="..."&lt;
+					    &lt;img class="fragment" width="300" height="450" src="..."&lt;
+					    &lt;img class="fragment" width="400" height="400" src="..."&lt;
 					  </div>
 					</code></pre>
 				</section>