[buildtools] update .gitignore for CIPD

Bug: 855791
Change-Id: Id4d8c98953d40635b8f1784ac5b147f932a2e42a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1530371
Reviewed-by: Nico Weber <thakis@chromium.org>
Commit-Queue: Nico Weber <thakis@chromium.org>
Auto-Submit: Takuto Ikuta <tikuta@chromium.org>
Cr-Commit-Position: refs/heads/master@{#641853}
1 file changed