Prefer builtins.path

Following the advice of Domen's nix.dev anti-patterns, I'm preferring something
like...

```nix
builtins.path { path = /path/to/some.where; name = "some.where"; }
```

...to

```nix
/path/to/some/where
```

While the former is more verbose, it will fail to build when the path doesn't
exist, which I prefer.

tools/simple_vim/default.nix

@@ -1,8 +1,13 @@
 { pkgs, ... }:
 
 let
+  configVim = builtins.path {
+    path = ./config.vim;
+    name = "config.vim";
+  };
+
   script = pkgs.writeShellScriptBin "simple_vim" ''
-    ${pkgs.vim}/bin/vim -u ${./config.vim}
+    ${pkgs.vim}/bin/vim -u ${configVim}
   '';
 in pkgs.stdenv.mkDerivation {
   name = "simple_vim";