Migrate Gitlab Users from an older version to a newer?

I am currently migrating gitlab from version 6.x to the newest 7.2.0 . On the old machine I have Ubuntu 12.04 installed and on the new one of course 14.04.
I copy the bare repos and do the rake migration to create the projects in gitlab.
But how can I copy the users? So far I don’t see a valid option between 2 different versions. Any ideas?