html5as: Fix downloader using wrong keyword for target

4 jobs for 1.0
Status Job ID Name Coverage
  External
failed ERP5.StandaloneDeploymentScriptTest-Debian.Stretch

failed SlapOS-Master.StandaloneDeploymentScriptTest-Debian.Stretch

failed Wendelin.StandaloneDeploymentScriptTest-Debian.Buster.Master

failed Wendelin.StandaloneDeploymentScriptTest-Debian.Stretch