glock: add license

pkgs/development/tools/glock/default.nix

···
   meta = with stdenv.lib; {
     homepage = https://github.com/robfig/glock;
     description = "A command-line tool to lock Go dependencies to specific revisions";
+    license = licenses.mit;
     maintainers = [ maintainers.rushmorem ];
   };
 }