bpo-36324:  Apply review comments from Allen Downey (GH-15693)

diff --git a/Misc/ACKS b/Misc/ACKS
index ce427b8..6318998 100644
--- a/Misc/ACKS
+++ b/Misc/ACKS
@@ -416,6 +416,7 @@
 Yves Dorfsman
 Michael Dorman
 Steve Dower
+Allen Downey
 Cesar Douady
 Dean Draayer
 Fred L. Drake, Jr.