code: func (s *RepositoriesService) ListLanguages(ctx context.Context, owner string, repo string) (map[string]int, *Response, error) {
  	u := fmt.Sprintf("repos/%v/%v/languages", owner, repo)
  	req, err := s.client.NewRequest("GET", u, nil)
  	if err != nil {
  		return nil, nil, err
  	}
  
  	languages := make(map[string]int)
  	resp, err := s.client.Do(ctx, req, &languages)
  	if err != nil {
  		return nil, resp, err
  	}
  
  	return languages, resp, nil
  }
docs: // ListLanguages lists languages for the specified repository. The returned map
  // specifies the languages and the number of bytes of code written in that
  // language. For example:
  //
  //     {
  //       "C": 78769,
  //       "Python": 7769
  //     }
  //
  // GitHub API docs: https://developer.github.com/v3/repos/#list-languages