Update flake.nix to use latest agda.nix (#994)

* Update flake.nix to use latest agda.nix

* Update nixpkgs

* Add x86_64-darwin to systems

* Use fake HOME in python script environment

See https://nixos.org/manual/nixpkgs/stable/#sec-language-texlive-lualatex-font-cache

Author: carlostome

build-tools/nix/mkdocs.nix

@@ -60,7 +60,7 @@ mkDerivation {
   buildPhase = ''
     runHook preBuild
     mkdir -p dist
-    python ./build-tools/scripts/md/build.py --run-agda
+    env HOME=$(mktemp -d) python ./build-tools/scripts/md/build.py --run-agda
     (cd _build/md/mkdocs/; mkdocs build --site-dir ../../../dist/site)
     runHook postBuild
   '';