GitLab

Switches the "Mac FYI Experimental Retina Release (AMD)" and
"Mac FYI Experimental Retina Release (NVIDIA)" builders to run tests on
10.13.6.

Bug: 868032
Change-Id: Ice3945b56ae57260910970188d81266b6f4b2355
Reviewed-on: https://chromium-review.googlesource.com/1158984Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Brian Sheedy <bsheedy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#579900}