darwin: Ensure vim is default editor

nix-darwin sets `nano` as the default. :(

9e7c20ffd0/modules/environment/default.nix (L181)

darwin/darwin.nix

@@ -1,16 +1,20 @@
 { pkgs, system, ... }: {
-  # List packages installed in system profile. To search by name, run:
-  # $ nix-env -qaP | grep wget
-  environment.systemPackages = [
-    pkgs.vim
-  ];
+  environment = {
+    # We'll use Vim globally.
+    systemPackages = [
+      pkgs.vim
+    ];
+    variables.EDITOR = "${pkgs.vim}/bin/vim";
+  };
 
   # Auto upgrade nix package and the daemon service.
   services.nix-daemon.enable = true;
-  nix.package = pkgs.nix;
-
-  # Necessary for using flakes on this system.
-  nix.settings.experimental-features = "nix-command flakes";
+  nix = {
+    # Keep the latest version of Nix.
+    package = pkgs.nix;
+    # Necessary for using flakes on this system.
+    settings.experimental-features = "nix-command flakes";
+  };
 
   # Create /etc/zshrc that loads the nix-darwin environment.
   programs.zsh.enable = true;

flake.nix

@@ -105,7 +105,8 @@
           # System-wide configuration
           ./darwin/darwin.nix
           # Our provided home-manager configuration
-          home-manager.darwinModules.home-manager {
+          home-manager.darwinModules.home-manager
+          {
             home-manager = {
               useGlobalPkgs = true;
               useUserPackages = true;