nixfmt: format cabal2nix output on update script

Author: dyegoaurelio

pkgs/by-name/ni/nixfmt/update.sh

@@ -1,5 +1,5 @@
 #!/usr/bin/env nix-shell
-#!nix-shell -i bash -p cabal2nix curl jq
+#!nix-shell --pure -i bash -p cabal2nix curl cacert jq nixfmt
 #
 # This script will update the nixfmt derivation to the latest version using
 # cabal2nix.
@@ -22,6 +22,7 @@ EOF
 
 cabal2nix --jailbreak \
   "https://github.com/nixos/nixfmt/archive/${release_tag}.tar.gz" \
+  | nixfmt \
   >> "$derivation_file"
 
 echo "Finished."