[No JIRA] Pin greenkeeper-lockfile at 1.x.z
[No JIRA] Pin greenkeeper-lockfile at 1.x.z

Attempt to fix issues with greenkeeper on Travis. See
https://twitter.com/K0nserv/status/1021386978133266432.

Skyscanner/backpack,Skyscanner/backpack,Skyscanner/backpack