removed shutdown() function

For issue related to :
https://github.com/barryvdh/laravel-debugbar/issues/237

exception 'Symfony\Component\Debug\Exception\FatalErrorException' with message 'Call to undefined method Illuminate\Foundation\Application::shutdown()' in /barryvdh/laravel-debugbar/src/ServiceProvider.php:24

As the function shutdown() is removed from laravel 5