yum is deprecated; use dnf in util function

dotfiles/bash/main.bashrc

     local bname
     for bname in "$@";
     do
-        yum provides "*bin/$bname" \
+        dnf provides "*bin/$bname" \
           | grep '^.' \
           | grep -E '^[0-9a-zA-Z_:.-]+ :'
     done