Fix syntax error

celery/managers.py

@@ -65,9 +65,8 @@ class PeriodicTaskManager(models.Manager):
         for task_name, task in periodic_tasks.items():
             task_meta, created = self.get_or_create(name=task_name)
             # task_run.every must be a timedelta object.
-            run_every_drifted = task.run_every + \
-                                    timedelta(seconds=SERVER_DRIFT)
-            run_at = task_meta.last_run_at + task.run_every
+            run_every_drifted = task.run_every + SERVER_DRIFT
+            run_at = task_meta.last_run_at + run_every_drifted
             if datetime.now() > run_at:
                 waiting.append(task_meta)
         return waiting