code: func (s *SearchService) Labels(ctx context.Context, repoID int64, query string, opt *SearchOptions) (*LabelsSearchResult, *Response, error) {
  	result := new(LabelsSearchResult)
  	resp, err := s.search(ctx, "labels", &searchParameters{RepositoryID: &repoID, Query: query}, opt, result)
  	return result, resp, err
  }
docs: // Labels searches labels in the repository with ID repoID via various criteria.
  //
  // GitHub API docs: https://developer.github.com/v3/search/#search-labels