Give people one more month before we make 3.6 a hard requirement.

Change-Id: Ieb471b917c5ef5b9cb20b321305c4c13af675109
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2575635Reviewed-by: Michael Mortensen <mmortensen@google.com>
Commit-Queue: Mike Frysinger <vapier@chromium.org>