fix for 3.8

Author: chadrik

src/rez/utils/data_utils.py

@@ -10,11 +10,10 @@
 import os.path
 import json
 import functools
-from collections.abc import MutableMapping
 
 from rez.vendor.schema.schema import Schema, Optional
 from threading import Lock
-from typing import Any, Callable, Generic, TypeVar, TYPE_CHECKING
+from typing import Any, Callable, Generic, MutableMapping, TypeVar, TYPE_CHECKING
 
 T = TypeVar("T")