Add missing `@since` tag

   * A custom JSON-LD document loader factory.  By default, this uses

   * the built-in cache-backed loader that fetches remote documents over

   * HTTP(S).

   * @since 1.4.0

   */

  documentLoaderFactory?: DocumentLoaderFactory;

  /**

   * A custom JSON-LD context loader factory.  By default, this uses the same

   * loader as the document loader.

   * @since 1.4.0

   */

  contextLoaderFactory?: DocumentLoaderFactory;