Import ContextDecorator from contextlib

Will be removed on Django 3.0

orchestra/contrib/orchestration/managers.py

@@ -1,14 +1,14 @@
 import sys
+from contextlib import ContextDecorator
 from threading import local
 
 from django.contrib.admin.models import LogEntry
-from django.db.models.signals import pre_delete, post_save, m2m_changed
+from django.db.models.signals import m2m_changed, post_save, pre_delete
 from django.dispatch import receiver
-from django.utils.decorators import ContextDecorator
 
 from orchestra.utils.python import OrderedSet
 
-from . import manager, Operation, helpers
+from . import Operation, helpers, manager
 from .middlewares import OperationsMiddleware
 from .models import BackendLog, BackendOperation