Set mac_sdk_min=10.13 for CommandBuffer builds

The default SDK version was changed in
https://chromium-review.googlesource.com/c/chromium/src/+/1711106, but
our bots don't have that version yet. This is causing failed rolls,
e.g. https://skia-review.googlesource.com/c/skia/+/231071.

The DEPS change was cherry-picked from
https://skia-review.googlesource.com/c/skia/+/231071.

Change-Id: Iddfa0c7cb8ef676bf6f6b2093c120afdd33513f7
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/231097
Auto-Submit: Ben Wagner aka dogben <benjaminwagner@google.com>
Reviewed-by: Eric Boren <borenet@google.com>
Commit-Queue: Ben Wagner aka dogben <benjaminwagner@google.com>
4 files changed