create-release: use GNU sed on macOS

Author: Enzime

.gitignore

@@ -1,3 +1,3 @@
-result
+result*
 /.direnv
 /docs/book

scripts/create-release.sh

@@ -1,6 +1,7 @@
-#!/usr/bin/env bash
+#!/usr/bin/env nix
+#! nix shell nixpkgs#bash nixpkgs#gnused --command bash
 
-set -eu -o pipefail
+set -euo pipefail
 
 SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" >/dev/null && pwd)"
 cd "$SCRIPT_DIR/.."