software/jupyter: move to python 3

See merge request !868
4 jobs for cythonplus in 0 seconds
Status Job ID Name Coverage
  External
passed SlapOS.SlapRunner.ResilienceTest-Master

00:25:27

failed SlapOS.SlapRunner.ResilienceTest-Master.ERP5

00:25:33

passed SlapOS.SoftwareReleases.IntegrationTest-Master.Python2

05:47:45

failed SlapOS.SoftwareReleases.IntegrationTest-Master.Python3

05:19:15