Fix incorrect json in gatekeeper_trees.json.
Fix incorrect json in gatekeeper_trees.json.

BUG=394961
TBR=iannucci@chromium.org

Review URL: https://codereview.chromium.org/407073007

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@284780 0039d316-1c4b-4281-b951-d872f2087c98

eunchong/build,eunchong/build,eunchong/build,eunchong/build