wasabibackend: Use nixpkgs-fmt instead of nixfmt

pkgs/applications/blockchains/wasabibackend/create_deps.sh

···
 #! /usr/bin/env nix-shell
-#! nix-shell -i bash -p dotnet-sdk_3 jq xmlstarlet curl nixfmt
+#! nix-shell -i bash -p dotnet-sdk_3 jq xmlstarlet curl nixpkgs-fmt
 set -euo pipefail
 
 # Run this script to generate deps.nix
···
 
 exec 6>&-
 
-nixfmt "$deps_file"
+nixpkgs-fmt "$deps_file"