Use Rsync for syncing docs dir

cp -rl was wonky on macOS. rsync worked much better.
Makes the release available on http://127.0.0.1:4000/releases/dev/release/

package.json

@@ -44,7 +44,7 @@
     "test": "npm run test-node && npm run test-headless && npm run test-webworker",
     "check-dependencies": "dependency-check package.json --no-dev --ignore-module esm",
     "build": "node ./build.cjs",
-    "dev-docs": "cd docs; cp -rl release-source releases/dev; npm run serve-docs",
+    "dev-docs": "cd docs; rsync -r --delete release-source/ releases/dev; npm run serve-docs",
     "build-docs": "cd docs; bundle exec jekyll build",
     "serve-docs": "cd docs; bundle exec jekyll serve --incremental --verbose --livereload",
     "lint": "eslint --max-warnings 101 '**/*.{js,cjs,mjs}'",