code: func (s *GitService) UpdateRef(ctx context.Context, owner string, repo string, ref *Reference, force bool) (*Reference, *Response, error) {
  	refPath := strings.TrimPrefix(*ref.Ref, "refs/")
  	u := fmt.Sprintf("repos/%v/%v/git/refs/%v", owner, repo, refPath)
  	req, err := s.client.NewRequest("PATCH", u, &updateRefRequest{
  		SHA:   ref.Object.SHA,
  		Force: &force,
  	})
  	if err != nil {
  		return nil, nil, err
  	}
  
  	r := new(Reference)
  	resp, err := s.client.Do(ctx, req, r)
  	if err != nil {
  		return nil, resp, err
  	}
  
  	return r, resp, nil
  }
docs: // UpdateRef updates an existing ref in a repository.
  //
  // GitHub API docs: https://developer.github.com/v3/git/refs/#update-a-reference