software/dufs: version up 0.31.0

4 jobs for master
Status Job ID Name Coverage
  External
failed ERP5.StandaloneDeploymentScriptTest-Debian.Stretch

failed SlapOS-Master.StandaloneDeploymentScriptTest-Debian.Stretch

passed Wendelin.StandaloneDeploymentScriptTest-Debian.Buster.Master

failed Wendelin.StandaloneDeploymentScriptTest-Debian.Stretch