chromium/buildtools repo was moved and broke the V8 auto-roller.

This CL corrects the old-path.
Failed-Roll: https://chromium-review.googlesource.com/c/v8/v8/+/1459743

R=machenbach@chromium.org,sergiyb@chromium.org
CC=​yangguo@chromium.org

Bug: chromium:930050
Change-Id: I969c73c13bfa996b1010971c37d9325c22048c0a
Reviewed-on: https://chromium-review.googlesource.com/c/1460464
Commit-Queue: Tamer Tas <tmrts@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59447}