Fix typo in max-age attribute for Set-Cookie header response.

(and make it lowercase to be consistent)

Change-Id: I942bf3d65f8bff67dceae35fcef63ee573943f50
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2551619
Reviewed-by: Steven Bingler <bingler@chromium.org>
Reviewed-by: Robert Ma <robertma@chromium.org>
Commit-Queue: Mike Taylor <miketaylr@chromium.org>
Cr-Commit-Position: refs/heads/master@{#829698}
diff --git a/cookies/resources/helpers.py b/cookies/resources/helpers.py
index 1002b84..47f40b4 100644
--- a/cookies/resources/helpers.py
+++ b/cookies/resources/helpers.py
@@ -36,7 +36,7 @@
     return (b"Set-Cookie", b"; ".join((attrs)))
 
 def makeDropCookie(name, secure):
-    attrs = {b"MaxAge": 0, b"path": b"/"}
+    attrs = {b"max-age": 0, b"path": b"/"}
     if secure:
         attrs[b"secure"] = b""
     return makeCookieHeader(name, b"", attrs)