code: func (w *Writer) Flush() error {
  	w.seq++
  	w.writePending()
  	if w.err != nil {
  		return w.err
  	}
  	if w.f != nil {
  		w.err = w.f.Flush()
  		return w.err
  	}
  	return nil
  }
docs: // Flush finishes the current journal, writes to the underlying writer, and
  // flushes it if that writer implements interface{ Flush() error }.