stack/slapos: Pin traitlets

The version >=5 is not python2 compatible.
7 jobs for 1.0 in 0 seconds
Status Job ID Name Coverage
  External
passed SlapOS.SlapRunner.ResilienceTest-Master

00:26:29

failed SlapOS.SlapRunner.ResilienceTest-Master.ERP5

00:23:12

failed SlapOS.SoftwareReleases.IntegrationTest-Master.Python2

12:11:26

failed SlapOS.SoftwareReleases.IntegrationTest-Master.Python3

38:09:14

failed SlapOS.SlapRunner.ResilienceTest-Master.ERP5

00:19:00

failed SlapOS.SoftwareReleases.IntegrationTest-Master.Python2

07:15:42

failed SlapOS.SoftwareReleases.IntegrationTest-Master.Python3

06:00:20