collections.abc python 3.8

Summary:
In python 3.7 collections.abc warns when importing abc classes from `collections`
In 3.8 this will not work at all.

This changes all code using abc's from collections to attempt to import from `collections.abc`

I am not fixing existing lint's don't ask, if `arc lint` auto-fixed I accepted, except for spelling in code.

Reviewed By: lisroach

Differential Revision: D15461049

fbshipit-source-id: ac2bf2ec8cffacd8ba5572882b0832bbf99a1646

fairseq/data/data_utils.py

@@ -8,7 +8,10 @@
 import contextlib
 import os
 import numpy as np
-from collections import Iterable
+try:
+    from collections.abc import Iterable
+except ImportError:
+    from collections import Iterable
 
 
 def infer_language_pair(path):