PHP Fatal error: Class 'Barryvdh\DomPDF\ServiceProvider' not found laravel 5.5

i did follow all the steps

1. composer require barryvdh/laravel-dompdf

2. 'providers' => [ .... Barryvdh\DomPDF\ServiceProvider::class, ], 'aliases' => [ .... 'PDF' => Barryvdh\DomPDF\Facade::class, ],

   i don't know what i should do any help or suggestion , please!

via Chebli Mohamed