[refactor] Modified collections to collections.abc in import (#988)

fairscale/optim/grad_scaler.py

@@ -3,7 +3,8 @@
 # This source code is licensed under the MIT license found in the
 # LICENSE file in the root directory of this source tree.
 
-from collections import abc, defaultdict
+from collections import defaultdict
+import collections.abc as abc
 from enum import Enum
 import logging
 from typing import Any, Dict, List, Optional, Union

fairscale/utils/params.py

@@ -3,7 +3,7 @@
 # This source code is licensed under the BSD license found in the
 # LICENSE file in the root directory of this source tree.
 
-from collections import abc
+import collections.abc as abc
 from math import inf
 from typing import Any, Callable, Dict, List, Optional