v1: STORE State error

[Emocjl]

In version 1.2.1，when i use “ err = connection.Store(seq, item, flags, nil)” ，an error has been reported

[Emocjl]

func updateEmailStatus(c *client.Client, seqNum int) {
	set := new(imap.SeqSet)
	set.AddNum(uint32(seqNum))
	done := make(chan error, 1)
	go func() {
		done <- c.Store(set, imap.AddFlags, []interface{}{imap.SeenFlag}, nil)
	}()
	select {
	case err := <-done:
		if err != nil {
			log.Fatal(err)
		}
	}
}