Update Flash Fixture doc

Updated fash fixture doc to actual behavior as #912

docs/chapter-06.rst

@@ -345,13 +345,7 @@ and in the template:
 
 .. code:: html
 
-   ...
-   <div id="py4web-flash"></div>
-   ...
-   <script src="js/utils.js"></script>
-   [[if globals().get('flash'):]]
-   <script>utils.flash([[=XML(flash)]]);</script>
-   [[pass]]
+   <flash-alerts class="padded" data-alert="[[=globals().get('flash','')]]"></flash-alerts>
 
 By setting the value of the message in the flash helper, a flash
 variable is returned by the action and this triggers the JS in the