async function packageExtension() {
  await fs.promises.mkdir(packagePath, {recursive: true});

  return new Promise((resolve, reject) => {
    const archive = archiver('zip', {
      zlib: {level: 9},
    });

    const outPath = `${packagePath}/lighthouse-${manifestVersion}.zip`;
    const writeStream = fs.createWriteStream(outPath);
    writeStream.on('finish', resolve);
    writeStream.on('error', reject);

    archive.pipe(writeStream);
    archive.directory(distDir, false);
    archive.finalize();
  });
}
Put built extension into a zip file ready for install or upload to the
webstore.
@return {Promise<void>}