Heroku config:set App_KEY 后提示 No App specified，是怎么回事？

如下

vagrant@homestead:~/Code/laravel$ php artisan key:generate
Application key [base64:3KGblmTyBHKdezQ+/seGYYcUPUyl+fajjypo5kGBHRw=] set successfully.
vagrant@homestead:~/Code/laravel$ heroku config:set APP_KEY=base64:3KGblmTyBHKdezQ+/seGYYcUPUyl+fajjypo5kGBHRw=
 ▸    heroku-cli: update available from 6.13.19 to 6.15.39-44c1447
 ▸    No app specified