update nix dependencies with niv-update

* changes to nix-build output:

No version or selection state changes.
Closure size: 13 -> 13 (0 paths added, 0 paths removed, delta +0, disk usage +0B).

* changes to nix-shell output:

No version or selection state changes.
Closure size: 1142 -> 1142 (4 paths added, 4 paths removed, delta +0, disk usage +24B).

nix/sources.json

@@ -5,10 +5,10 @@
         "homepage": "",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "e6ab46982debeab9831236869539a507f670a129",
-        "sha256": "0ykjrirzxwf51d8i4pfhr5i3jyyfzn33vappdwaync0yg5i58dp4",
+        "rev": "5faab29808a2d72f4ee0c44c8e850e4e6ada972f",
+        "sha256": "0z607san2f8ig52834f2fc3xazk9ss7lsyl12j7c9psn337ypna4",
         "type": "tarball",
-        "url": "https://github.com/NixOS/nixpkgs/archive/e6ab46982debeab9831236869539a507f670a129.tar.gz",
+        "url": "https://github.com/NixOS/nixpkgs/archive/5faab29808a2d72f4ee0c44c8e850e4e6ada972f.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "olderIdeaNixpkgs": {