don't load kitten picture from third party site

Author: paskal

frontend/apps/remark42/templates/400x400.jpeg

@@ -348,7 +348,7 @@ <h2 id="Images">Images</h2>
           <p>If you want to embed images, this is how you do it:</p>
           <pre>![Image of my cat](https://placekitten.com/400/400)</pre>
           <p>
-            <img src="https://placekitten.com/400/400" width="400" height="400" alt="" />
+            <img src="400x400.jpeg" width="400" height="400" alt="" />
           </p>
 
           <h2 id="Code">Code</h2>