ldc-legaulois/app/Http/Requests/UpdateArticle.php

<?php

namespace App\Http\Requests;

class UpdateArticle extends StoreArticle
{

    public function rules()
    {
        return array_merge(
            parent::rules(),
            [
                'slug' => 'required|unique:articles,slug,' . $this->article->id . '|max:255',
            ]
        );
    }
}