code: func (s *ShallowStorage) SetShallow(commits []plumbing.Hash) error {
  	f, err := s.dir.ShallowWriter()
  	if err != nil {
  		return err
  	}
  
  	defer ioutil.CheckClose(f, &err)
  	for _, h := range commits {
  		if _, err := fmt.Fprintf(f, "%s\n", h); err != nil {
  			return err
  		}
  	}
  
  	return err
  }
docs: // SetShallow save the shallows in the shallow file in the .git folder as one
  // commit per line represented by 40-byte hexadecimal object terminated by a
  // newline.