bump nixpkgs, esp. for linux 5.10.103

nixpkgs.json

 {
   "name": "source",
-  "url": "https://releases.nixos.org/nixos/21.11/nixos-21.11.336182.a25df4c2b79/nixexprs.tar.xz",
-  "sha256": "02lpc1q7hf00z5llwbz0a48nk5v36fc3c84axbaww7m8vgpkd20m"
-}
\ No newline at end of file
+  "url": "https://releases.nixos.org/nixos/21.11/nixos-21.11.336340.2ebb6c1e5ae/nixexprs.tar.xz",
+  "sha256": "1hi47fq801v2bk7ms50sz7a8744zfkkk27kxjpbxzv1n6k0n1w1q"
+}