docs: fix middleware img (#7110)

Author: Matt Maribojoc

docs/content/3.middleware/2.guides/3.extensions.md

@@ -65,7 +65,7 @@ const extension = {
 Middleware extensions allow you to extend your Express.js server, register additional API endpoints, or hook into the
 lifecycle of a request sent to a given Server Middleware integration from the application.
 
-<img alt="Middleware Data Flow" src="./img/extensions/data-flow.svg" class="mx-auto" />
+<img alt="Middleware Data Flow" src="../img/extensions/data-flow.svg" class="mx-auto" />
 
 ## Use Cases