docs: missing bracket

docs/guide/advanced/navigation-guards.md

@@ -45,6 +45,7 @@ And can optionally return any of the following values:
       return { name: 'Login' }
     }
   })
+  ```
 
 It's also possible to throw an `Error` if an unexpected situation was met. This will also cancel the navigation and call any callback registered via [`router.onError()`](../../api/#onerror).