greenkeeper-lockfile 1.0.0

This package used to be greenkeeper-shrinkwrap.
In the light of npm5 and it's new package-lock.json file we made two changes:

1. Support package-lock.json (and the npm5 package if present)
2. Rename this package to the more generic greenkeeper-lockfile, because it now supports both npm-shrinkwrap.json and package-lock.json files.