flake: use new devshell format

flake.nix

@@ -37,18 +37,23 @@
                 src = pkgs.lib.cleanSource ./.;
               };
           });
-      devShell = forAllSystems ({ system, pkgs, fpkgs }:
+      devShells = forAllSystems
+        ({ system, pkgs, fpkgs }:
           let
             ffpkgs = fpkgs.complete;
           in
-        pkgs.mkShell {
+          {
+            default = pkgs.mkShell
+              {
                 buildInputs = [
                   ffpkgs.cargo
                   ffpkgs.clippy
                   ffpkgs.rust-src
                   ffpkgs.rustc
                   ffpkgs.rustfmt
+                  pkgs.wgo
                 ];
+              };
           });
     };
 }