fix linter

Signed-off-by: memleakd <121398829+memleakd@users.noreply.github.com>

Author: memleakd

user_guide_src/source/models/model/073.php

@@ -4,7 +4,7 @@
     $account->balance -= 100;
 
     if (! $model->save($account)) {
-        throw new RuntimeException('Unable to save the account.');
+        throw new \RuntimeException('Unable to save the account.');
     }
 
     return true;