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

Change-Id: I696bf3f0edbe64d6294dd626fc9ff16c9e44fd87
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2570017Reviewed-by: Michael Mortensen <mmortensen@google.com>
Commit-Queue: Mike Frysinger <vapier@chromium.org>