update nixpkgs

nix/sources.json

@@ -30,15 +30,15 @@
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "nixpkgs": {
-        "branch": "release-21.05",
+        "branch": "release-21.11",
         "description": "Nix Packages collection",
         "homepage": "",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "6c0c30146347188ce908838fd2b50c1b7db47c0c",
-        "sha256": "05bh6kw7jzfxpvhndsg6swgbk1x7fsgnwahzm3jgd61rsvknhn93",
+        "rev": "a1ea9a03542ac3ae764cb4e671901e650226178c",
+        "sha256": "03xb0axggl95xrynyiyhrzsx5c9l7iy1rfhjqggklg72vrph44rn",
         "type": "tarball",
-        "url": "https://github.com/NixOS/nixpkgs/archive/6c0c30146347188ce908838fd2b50c1b7db47c0c.tar.gz",
+        "url": "https://github.com/NixOS/nixpkgs/archive/a1ea9a03542ac3ae764cb4e671901e650226178c.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "simple-nixos-mailserver": {