Update hash in pinned.nix

nix/pinned.nix

 import (
   builtins.fetchTarball {
     url = "https://github.com/NixOS/nixpkgs/archive/21.05.tar.gz";
-    sha256 = "0182ys095dfx02vl2a20j1hz92dx3mfgz2a6fhn31bqlp1wa8hlq";
+    sha256 = "1ckzhh24mgz6jd1xhfgx0i9mijk6xjqxwsshnvq789xsavrmsc36";
   }
 )