code: func writeLock(chartpath string, lock *chartutil.RequirementsLock) error {
  	data, err := yaml.Marshal(lock)
  	if err != nil {
  		return err
  	}
  	dest := filepath.Join(chartpath, "requirements.lock")
  	return ioutil.WriteFile(dest, data, 0644)
  }
docs: // writeLock writes a lockfile to disk