code: func (s *GitService) DeleteRef(ctx context.Context, owner string, repo string, ref string) (*Response, error) {
  	ref = strings.TrimPrefix(ref, "refs/")
  	u := fmt.Sprintf("repos/%v/%v/git/refs/%v", owner, repo, url.QueryEscape(ref))
  	req, err := s.client.NewRequest("DELETE", u, nil)
  	if err != nil {
  		return nil, err
  	}
  
  	return s.client.Do(ctx, req, nil)
  }
docs: // DeleteRef deletes a ref from a repository.
  //
  // GitHub API docs: https://developer.github.com/v3/git/refs/#delete-a-reference