fix dns reject action doc

[PuerNya]

f2687a7 中的 dns action reject 行为已变更，建议修改文档描述

sing-box/dns/router.go

Lines 260 to 268 in f2687a7

	case C.RuleActionRejectMethodDefault:
	return &mDNS.Msg{
	MsgHdr: mDNS.MsgHdr{
	Id: message.Id,
	Rcode: mDNS.RcodeRefused,
	Response: true,
	},
	Question: []mDNS.Question{message.Question[0]},
	}, nil