Build: Properly nest gitignore for luci-go

The directory tools/luci-go is now under a subtreed repo mirror and
should have its own gitignore file.

Bug: chromium:754168
Change-Id: I716b6c853f04c9284287e417500a821c01dab8c4
Reviewed-on: https://chromium-review.googlesource.com/707146
Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>
Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#507430}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: d137552822699e748d38d7a86e97ba6e2bce093e
1 file changed