Update github.com/miekg/dns to pick up fix for CVE-2019-19794.

I noticed this was out of date using 'snyk test' on the main repository.

vendor/github.com/miekg/dns/acceptfunc.go

@@ -6,22 +6,30 @@ type MsgAcceptFunc func(dh Header) MsgAcceptAction
 
 // DefaultMsgAcceptFunc checks the request and will reject if:
 //
-// * isn't a request (don't respond in that case).
+// * isn't a request (don't respond in that case)
+//
 // * opcode isn't OpcodeQuery or OpcodeNotify
+//
 // * Zero bit isn't zero
+//
 // * has more than 1 question in the question section
+//
 // * has more than 1 RR in the Answer section
+//
 // * has more than 0 RRs in the Authority section
+//
 // * has more than 2 RRs in the Additional section
+//
 var DefaultMsgAcceptFunc MsgAcceptFunc = defaultMsgAcceptFunc
 
 // MsgAcceptAction represents the action to be taken.
 type MsgAcceptAction int
 
 const (
-	MsgAccept MsgAcceptAction = iota // Accept the message
-	MsgReject                        // Reject the message with a RcodeFormatError
-	MsgIgnore                        // Ignore the error and send nothing back.
+	MsgAccept               MsgAcceptAction = iota // Accept the message
+	MsgReject                                      // Reject the message with a RcodeFormatError
+	MsgIgnore                                      // Ignore the error and send nothing back.
+	MsgRejectNotImplemented                        // Reject the message with a RcodeNotImplemented
 )
 
 func defaultMsgAcceptFunc(dh Header) MsgAcceptAction {
@@ -32,12 +40,9 @@ func defaultMsgAcceptFunc(dh Header) MsgAcceptAction {
 	// Don't allow dynamic updates, because then the sections can contain a whole bunch of RRs.
 	opcode := int(dh.Bits>>11) & 0xF
 	if opcode != OpcodeQuery && opcode != OpcodeNotify {
-		return MsgReject
+		return MsgRejectNotImplemented
 	}
 
-	if isZero := dh.Bits&_Z != 0; isZero {
-		return MsgReject
-	}
 	if dh.Qdcount != 1 {
 		return MsgReject
 	}