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:

Version changes:
[U*]  #1  vscodium  1.80.0.23188 -> 1.80.1.23194
Closure size: 1142 -> 1142 (2 paths added, 2 paths removed, delta +0, disk usage +768B).

nix/sources.json

@@ -5,10 +5,10 @@
         "homepage": "",
         "owner": "NixOS",
         "repo": "nixpkgs",
-        "rev": "6cee3b5893090b0f5f0a06b4cf42ca4e60e5d222",
-        "sha256": "088yi2181nfyxalkg0g84jv4jcmxclihnrcaywfmxqzz61vr8x4f",
+        "rev": "684c17c429c42515bafb3ad775d2a710947f3d67",
+        "sha256": "1gvi4vlq1cxyi3w2mqm939c5ib5509a2ycpwyki51jdgcpkh4x9c",
         "type": "tarball",
-        "url": "https://github.com/NixOS/nixpkgs/archive/6cee3b5893090b0f5f0a06b4cf42ca4e60e5d222.tar.gz",
+        "url": "https://github.com/NixOS/nixpkgs/archive/684c17c429c42515bafb3ad775d2a710947f3d67.tar.gz",
         "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
     },
     "olderIdeaNixpkgs": {