Use dnf instead of yum
    
    I left the instructions for yum-langpacks around, because I'm not sure
    how the dnf replacement looks. But all references to yum-the-executable
    are gone.
    
    https://fedoraproject.org/wiki/Changes/Retire_YUM_3
    https://bugzilla.redhat.com/show_bug.cgi?id=1682910