Update configuration files

Signed-off-by: Oliver Davies <oliver@oliverdavies.uk>

.envrc

@@ -1 +1 @@
-use flake
+use flake .

flake.nix

@@ -1,19 +1,26 @@
 {
-  inputs.nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
+  inputs = {
+    devshell.url = "github:numtide/devshell";
+    flake-parts.url = "github:hercules-ci/flake-parts";
+    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
+  };
 
-  outputs = inputs:
-    let
-      system = "x86_64-linux";
-      pkgs = import inputs.nixpkgs { inherit system; };
-    in
-    {
-      devShells.${system}.default =
-        with pkgs;
-        mkShell {
-          buildInputs = [
-            go
-            gopls
-          ];
+  outputs =
+    inputs:
+    inputs.flake-parts.lib.mkFlake { inherit inputs; } {
+      imports = [ inputs.devshell.flakeModule ];
+
+      systems = [ "x86_64-linux" ];
+
+      perSystem =
+        { pkgs, ... }:
+        {
+          devshells.default = {
+            packages = with pkgs; [
+              go
+              gopls
+            ];
+          };
         };
     };
 }