stack/slapos.cfg: version up rubygemsrecipe to 0.4.2

- rubygemsrecipe deployment mode now depends on `allow-picked-versions` by default
6 jobs for master in 0 seconds
Status Job ID Name Coverage
  External
passed SlapOS.Eggs.UnitTest-Master.Python2

00:09:15

passed SlapOS.Eggs.UnitTest-Master.Python3

00:16:19

passed SlapOS.SlapRunner.ResilienceTest-Master

00:21:32

failed SlapOS.SlapRunner.ResilienceTest-Master.ERP5

00:24:55

failed SlapOS.SoftwareReleases.IntegrationTest-Master.Python2

07:16:23

failed SlapOS.SoftwareReleases.IntegrationTest-Master.Python3

05:08:58