failed to git rev-parse repository

[KeyboardNerd]

Description of Problem / Feature Request

It seems gitutil.go is buggy, when every updater is retrieving git repo it has this:

{
  "Event": "failed to git rev-parse repository",
  "Level": "error",
  "Location": "gitutil.go:52",
  "Time": "2018-10-16 20:48:57.603876",
  "error": "exit status 128",
  "output": "fatal: not a git repository (or any of the parent directories): .git\n",
  "path": "/var/folders/s0/k5c638mx7cqd__vjjqb1qdkw0000gn/T/ubuntuUpdater597390701"
}

Environment

• Clair version/image: master