terraform-providers: use nurl in update-provider script

#!/usr/bin/env nix-shell

#! nix-shell -i bash -p coreutils curl git jq moreutils nix nix-prefetch

#! nix-shell -i bash -p coreutils curl git jq moreutils nix nurl

# shellcheck shell=bash

# vim: ft=sh

#

repo_root=$(git rev-parse --show-toplevel)

generate_hash() {

  nix-prefetch -I nixpkgs="${repo_root}" \

    "{ sha256 }: (import ${repo_root} {}).terraform-providers.${provider}.$1.overrideAttrs (_: { inherit sha256; })"

  nurl --expr "(import ${repo_root} {}).terraform-providers.${provider}.$1"

}

echo_provider() {