Use plain source URL in Serving local files docs

docs/serving_local_files.md

@@ -22,5 +22,5 @@ local:///logos/evil_martians.png
 The URl for resizing this image to fit 300x200 will look like this:
 
 ```
-http://imgproxy.example.com/insecure/fit/300/200/no/0/bG9jYWw6Ly8vbG9n/b3MvZXZpbF9tYXJ0/aWFucy5wbmc.jpg
+http://imgproxy.example.com/insecure/fit/300/200/no/0/plain/local:///logos/evil_martians.png@jpg
 ```