Added code block.

upgrade.md

@@ -10,4 +10,4 @@
   to use `Illuminate\Routing\Controller`
 - Edit `app/controllers/BaseController.php` change `use Illuminate\Routing\Controllers\Controller;` to `use Illuminate\Routing\Controller;
 `
-- If you are overriding missingMethod in your controllers, add $method as the first parameter.
+- If you are overriding `missingMethod` in your controllers, add $method as the first parameter.