Fix image example receiving transition class names

Author: jlukic

server/documents/behaviors/visibility.html.eco

@@ -578,7 +578,7 @@ type        : 'UI Behavior'
       </div>
     </div>
 
-    <div class="visibility example">
+    <div class="visibility shown example">
       <h4 class="ui header">Lazy Loading Images</h4>
       <p>Visibility includes several shortcuts for setting up common visibility events. Using the setting <code>type: 'image'</code> will automatically attach events to an images <code>topVisible</code> to load the contents of <code>data-src</code> as <code>src</code>.</p>