"l5starter/core": "5.4.x-dev"
to your composer.json. Then run composer install or composer update.
Prettus\Repository\Providers\RepositoryServiceProvider::class,
Laracasts\Flash\FlashServiceProvider::class,
Collective\Html\HtmlServiceProvider::class,
L5Starter\Core\CoreServiceProvider::class,
'Form' => Collective\Html\FormFacade::class,
'Html' => Collective\Html\HtmlFacade::class,
'Flash' => Laracasts\Flash\Flash::class,