ms-sys: correct licence

pkgs/tools/misc/ms-sys/default.nix

···
     inherit version;
     description = "A program for writing Microsoft compatible boot records";
     homepage = http://ms-sys.sourceforge.net/;
-    license = licenses.gpl2;
+    license = licenses.gpl2Plus;
     maintainers = with maintainers; [ nckx ];
   };
 }