packages/building-rollup/plugins/rollup-plugin-modern-web/utils.js
function writeOutputHTML(dir, html) {
  const outputPath = pathJoin(dir, 'index.html');
  mkdirp.sync(path.dirname(outputPath));
  writeFileSync(outputPath, serialize(html));
}
function writeOutputHTML(dir, html) {
  const outputPath = pathJoin(dir, 'index.html');
  mkdirp.sync(path.dirname(outputPath));
  writeFileSync(outputPath, serialize(html));
}
Writes given HTML AST to output index.html