gnutar: add RossComputerGuy as maintainer

pkgs/tools/archivers/gnutar/default.nix

···
 
     license = lib.licenses.gpl3Plus;
 
-    maintainers = [ ];
+    maintainers = with lib.maintainers; [ RossComputerGuy ];
     mainProgram = "tar";
     platforms = lib.platforms.all;