Fix collections.iterable warning (keon#553)

nikhilhassija · keon · commit 816bec01d51a · 2019-10-16T16:57:05.000-07:00
diff --git a/algorithms/arrays/flatten.py b/algorithms/arrays/flatten.py
@@ -3,7 +3,7 @@
 Given an array that may contain nested arrays,
 produce a single resultant array.
 """
-from collections import Iterable
+from collections.abc import Iterable
 
 
 # return list
