Pin nixpkgs

default.nix

@@ -1,4 +1,8 @@
-with import <nixpkgs> {};
+with import (builtins.fetchTarball {
+  url = "https://github.com/NixOS/nixpkgs/tarball/b67bc34d4e3de1e89b8bb7cd6e375ba44f1ae8ca";
+  sha256 = "1q9a64bl5afflgpa2iaw1q7z7s08c8xq9w6lndlnc5c3siajrp8v";
+}) {};
+
 crystal.buildCrystalPackage rec {
   version = "0.1.0";
   pname = "TildesAutolinkerBot";