Prefer builtins.path

Thanks to the Nix anti-patterns documented here...

https://nix.dev/anti-patterns/language.html#reproducability-referencing-top-level-directory-with

...I'm cleaning up some of my Nix expressions. Read the article for more
context.

website/blog/default.nix

@@ -3,7 +3,7 @@
 pkgs.stdenv.mkDerivation {
   name = "blog.wpcarro.dev";
   buildInputs = with pkgs; [ hugo ];
-  src = ./.;
+  src = builtins.path { path = ./.; name = "blog"; };
   buildPhase = ''
     mkdir -p $out
     ${pkgs.hugo}/bin/hugo --minify --destination $out