nix: Update nixpkgs checkout/pin

Gets us go-1.16 by default and 1.17 available.

Signed-off-by: Manuel Mendez <mmendez@equinix.com>

shell.nix

@@ -1,10 +1,10 @@
 let _pkgs = import <nixpkgs> { };
 in { pkgs ? import (_pkgs.fetchFromGitHub {
   owner = "NixOS";
-  repo = "nixpkgs-channels";
-  #branch@date: nixpkgs-unstable@2020-09-11
-  rev = "6d4b93323e7f78121f8d6db6c59f3889aa1dd931";
-  sha256 = "0g2j41cx2w2an5d9kkqvgmada7ssdxqz1zvjd7hi5vif8ag0v5la";
+  repo = "nixpkgs";
+  #branch@date: nixpkgs-unstable@2021-11-12
+  rev = "2fbba4b4416446721ebfb2e0bfcc9e45d8ddb4d2";
+  sha256 = "1yw2p38pdvx63n21g6pmn79xjpxa93p1qpcadrlmg0j0zjnxkwr8";
 }) { } }:
 
 with pkgs;