don't use date time when modify a group

src/Application/Actions/Group/ModifyGroupAction.php

@@ -6,7 +6,6 @@ namespace App\Application\Actions\Group;
 use Psr\Http\Message\ResponseInterface as Response;
 use Psr\Http\Message\ServerRequestInterface as Request;
 use App\Domain\Group\Group ;
-use DateTime;
 
 class ModifyGroupAction extends GroupAction
 {