stack/slapos.cfg: fix eggs version for python3.7

This is a fixup of 5f6a2eb8.
6 jobs for 1.0
Status Job ID Name Coverage
  External
passed Cloudooo.UnitTest-Master

failed ERP5.StandaloneDeploymentScriptTest-Debian.Buster.Master

passed SlapOS.Eggs.UnitTest-Master.Python2

passed SlapOS.Eggs.UnitTest-Master.Python3

failed SlapOS.Eggs.UnitTest-Master.Python3Next

passed SlapOS.Theia.ResilienceTest-Master-ERP5