Add missing build dependencies to devshell.

I assume these were knocking around in the system environment on my mac.

flake.nix

@@ -6,29 +6,41 @@
     naersk.url = "github:nix-community/naersk";
     rust-overlay.url = "github:oxalica/rust-overlay";
   };
-   outputs = { self, nixpkgs, utils, naersk, devshell, rust-overlay }:
-    utils.lib.eachDefaultSystem (system:
-      let
+  outputs = {
+    self,
+    nixpkgs,
+    utils,
+    naersk,
+    devshell,
+    rust-overlay,
+  }:
+    utils.lib.eachDefaultSystem (system: let
       pkgs = import nixpkgs {inherit system;};
       naersk-lib = pkgs.callPackage naersk {};
-      in
-      {
+    in {
       defaultPackage = naersk-lib.buildPackage ./.;
 
       defaultApp = utils.lib.mkApp {
         drv = self.defaultPackage."${system}";
       };
-        devShell =
-        let pkgs = import nixpkgs {
+      devShells.default = let
+        pkgs = import nixpkgs {
           inherit system;
 
           overlays = [devshell.overlay (import rust-overlay)];
         };
       in
-        pkgs.devshell.mkShell {
-          packages = with pkgs; [ dhall (rust-bin.stable.latest.default.override {
+        pkgs.mkShell {
+          buildInputs = with pkgs; [
+            dhall
+            (rust-bin.stable.latest.default.override {
               extensions = ["rls"];
-          })];
+            })
+            pkg-config
+            libusb
+            openssl
+          ];
         };
+      formatter = pkgs.alejandra;
     });
 }