code: func (b *Bot) SetGroupPhoto(chat *Chat, p *Photo) error {
  	params := map[string]string{
  		"chat_id": chat.Recipient(),
  	}
  
  	respJSON, err := b.sendFiles("setChatPhoto", map[string]File{"photo": p.File}, params)
  	if err != nil {
  		return err
  	}
  
  	return extractOkResponse(respJSON)
  }
docs: // SetGroupPhoto should be used to update group photo.