fixed target iframe error

demos/postmessage2.html

@@ -10,7 +10,7 @@ iframe {
       <p><label for="message">Message</label><input type="text" name="message" value="my message" id="message" /> <input type="submit" />
       </p>
       <h2>Target iframe:</h2>
-      <iframe id="iframe" src="http://jsbin.com/uderi"></iframe>
+      <iframe id="iframe" src="http://jsbin.com/uderi/6"></iframe>
       </form>
     </article>
 <script>
@@ -27,4 +27,4 @@ addEvent(document.querySelector('form'), 'submit', function (e) {
 	// otherwise set the returnValue property of the original event to false (IE)
 	e.returnValue = false;
 });
-</script>
+</script>