Do report an error on yupdate overlay.

Before: it would silently do nothing
 (and I would wonder why my intent, `yupdate overlay create`, did not work)
Now: report an error, as intented

Author: mvidner

bin/yupdate

@@ -570,7 +570,7 @@ module YUpdate
       when "diff"
         OverlayFS.find_all.map(&:print_diff)
       else
-        InvalidCommand.new(command)
+        InvalidCommand.new(command).run
       end
     end
   end