flake: use new devshell format

flake.nix

@@ -37,19 +37,24 @@
                 src = pkgs.lib.cleanSource ./.;
               };
           });
-      devShell = forAllSystems ({ system, pkgs, fpkgs }:
+      devShells = forAllSystems
-        let
+        ({ system, pkgs, fpkgs }:
-          ffpkgs = fpkgs.complete;
+          let
-        in
+            ffpkgs = fpkgs.complete;
-        pkgs.mkShell {
+          in
-          buildInputs = [
+          {
-            ffpkgs.cargo
+            default = pkgs.mkShell
-            ffpkgs.clippy
+              {
-            ffpkgs.rust-src
+                buildInputs = [
-            ffpkgs.rustc
+                  ffpkgs.cargo
-            ffpkgs.rustfmt
+                  ffpkgs.clippy
-          ];
+                  ffpkgs.rust-src
-        });
+                  ffpkgs.rustc
+                  ffpkgs.rustfmt
+                  pkgs.wgo
+                ];
+              };
+          });
     };
 }