Add Source/core/gomacc.lock to .gitignore.

R=schenney@chromium.org
TBR=eseidel@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/108763003

git-svn-id: svn://svn.chromium.org/blink/trunk@163536 bbb929c8-8fbe-4397-9dbb-9b2b20218538