nixfmt: format cabal2nix output on update script

#!/usr/bin/env nix-shell

#!nix-shell -i bash -p cabal2nix curl jq

#!nix-shell --pure -i bash -p cabal2nix curl cacert jq nix

#

# This script will update the nixfmt derivation to the latest version using

# cabal2nix.

  "https://github.com/nixos/nixfmt/archive/${release_tag}.tar.gz" \

  >> "$derivation_file"

nix-shell "$script_dir/../../../../" \

  --run "treefmt --no-cache $derivation_file"

echo "Finished."