nimPackages.tkrzw: correct license metadata

https://git.sr.ht/~ehmry/nim-tkrzw/tree/20220922/item/src/tkrzw.nim#L1

pkgs/development/nim-packages/tkrzw/default.nix

···
   meta = with lib;
     src.meta // {
       description = "Nim wrappers over some of the Tkrzw C++ library";
-      license = lib.licenses.apsl20;
+      license = lib.licenses.asl20;
       maintainers = with lib.maintainers; [ ehmry ];
     };
 }