How to use the just-scripts.series.apply function in just-scripts

if (!fs.existsSync(configPath)) {
    return;
  }

  const config = JSON.parse(fs.readFileSync(configPath, 'utf8'));

  if (config && config.copyTo) {
    for (let destination in config.copyTo) {
      const sources = config.copyTo[destination];
      destination = path.resolve(process.cwd(), destination);
      tasks.push(copyTask(sources.map(src => expandSourcePath(src)), destination));
    }
  }

  return series.apply(null, tasks);
}