Error seeding database

[pacoorozco]

Describe the bug
After a fresh install, there is an error when i'm seeding the database:

$ docker-compose exec app php artisan migrate --seed

Nothing to migrate.
Seeding: UserTableSeeder

   Illuminate\Database\QueryException  : SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry 'user' for key 'users_username_unique' (SQL: insert into `users` (`name`, `username`, `email`, `password`, `role`, `updated_at`, `created_at`) values (User, user, user@example.com, $2y$10$arlg73tzxYgtawP6kSX46.lKEcesfZjz67sKoNSIQmfo1zuEbqcPu, user, 2020-03-22 13:31:53, 2020-03-22 13:31:53))

  at /var/www/vendor/laravel/framework/src/Illuminate/Database/Connection.php:669
    665|         // If an exception occurs when attempting to run a query, we'll format the error
    666|         // message to include the bindings with SQL, which will make this exception a
    667|         // lot more helpful to the developer instead of just the database's errors.
    668|         catch (Exception $e) {
  > 669|             throw new QueryException(
    670|                 $query, $this->prepareBindings($bindings), $e
    671|             );
    672|         }
    673| 

  Exception trace:

  1   PDOException::("SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry 'user' for key 'users_username_unique'")
      /var/www/vendor/laravel/framework/src/Illuminate/Database/Connection.php:463

  2   PDOStatement::execute()
      /var/www/vendor/laravel/framework/src/Illuminate/Database/Connection.php:463

  Please use the argument -v to see more details.