Use flake input for spork to avoid hash mismatches

flake.nix

@@ -4,11 +4,16 @@
     url = "git+https://codeberg.org/river/river.git?ref=main";
     flake = false;
   };
+  inputs.spork = {
+    url = "github:janet-lang/spork";
+    flake = false;
+  };
 
   outputs = inputs @ {
     self,
     nixpkgs,
     river,
+    spork,
   }: let
     systems = ["x86_64-linux" "aarch64-linux"];
     eachSystem = f:
@@ -35,12 +40,6 @@
         patches = [];
         doCheck = false;
       };
-      spork = pkgs.fetchFromGitHub {
-        owner = "janet-lang";
-        repo = "spork";
-        rev = "master";
-        hash = "sha256-gFUyrqkcjD34LZ9G7igaDwHnfIUUN9MzbvwEk9uWl1w=";
-      };
       janet-pm = pkgs.stdenv.mkDerivation {
         pname = "janet-pm";
         version = "1.1.1";