[Chromoting] Mac installer: Update Keystone to 1.2.13.40

Change-Id: I576dde6f0f55f9fe9ebaec0cfd6c763dd0995337
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1777077
Auto-Submit: Gary Kacmarcik <garykac@chromium.org>
Reviewed-by: Jamie Walch <jamiewalch@chromium.org>
Commit-Queue: Jamie Walch <jamiewalch@chromium.org>
Cr-Commit-Position: refs/heads/master@{#691874}