Fatal error: Uncaught Error: Class "yii\db\Migration" not found in /users/quirl/www/filemanager/spark/protected/humhub/modules/notification/migrations/m160517_132535_group.php:5 Stack trace: #0 {main} thrown in /users/quirl/www/filemanager/spark/protected/humhub/modules/notification/migrations/m160517_132535_group.php on line 5