bpo-30144: Import collections ABC from collections.abc rather than collections. (#1263)

diff --git a/Lib/cgi.py b/Lib/cgi.py
index 233a496..14d15a6 100755
--- a/Lib/cgi.py
+++ b/Lib/cgi.py
@@ -32,7 +32,7 @@
 # =======
 
 from io import StringIO, BytesIO, TextIOWrapper
-from collections import Mapping
+from collections.abc import Mapping
 import sys
 import os
 import urllib.parse