Add missing use \Exception

lib/Controller/TimeGateController.php

@@ -5,6 +5,7 @@ require_once __DIR__ . '/findMementos.php';
 require_once __DIR__ . '/datetimeConversion.php';
 require_once __DIR__ . '/getUrlParameter.php';
 
+use \Exception;
 use OCP\IRequest;
 use OCP\IServerContainer;
 use OCP\AppFramework\Controller;