Replace $.fn.bind with $.fn.on in alert docs

docs/_includes/js/alerts.html

@@ -64,7 +64,7 @@
     </table>
   </div><!-- /.table-responsive -->
 {% highlight js %}
-$('#my-alert').bind('closed.bs.alert', function () {
+$('#my-alert').on('closed.bs.alert', function () {
   // do something…
 })
 {% endhighlight %}