Fixing pre-commit things

stix2/v21/common.py

@@ -1,7 +1,6 @@
 """STIX 2.1 Common Data Types and Properties."""
 
 from collections import OrderedDict
-import copy
 
 from ..base import _STIXBase
 from ..custom import _custom_marking_builder
@@ -14,6 +13,7 @@ from ..properties import (
 )
 from ..utils import NOW, _get_dict
 
+
 class ExternalReference(_STIXBase):
     # TODO: Add link
     """For more detailed information on this object's properties, see