chore: fix some comments (#1547)

Signed-off-by: xiaoxiangxianzi <zhaoyizheng@outlook.com>

msg.go

@@ -714,7 +714,7 @@ func (h *MsgHdr) String() string {
 	return s
 }
 
-// Pack packs a Msg: it is converted to to wire format.
+// Pack packs a Msg: it is converted to wire format.
 // If the dns.Compress is true the message will be in compressed wire format.
 func (dns *Msg) Pack() (msg []byte, err error) {
 	return dns.PackBuffer(nil)

scan.go

@@ -1283,7 +1283,7 @@ func stringToCm(token string) (e, m uint8, ok bool) {
 			cmeters *= 10
 		}
 	}
-	// This slighly ugly condition will allow omitting the 'meter' part, like .01 (meaning 0.01m = 1cm).
+	// This slightly ugly condition will allow omitting the 'meter' part, like .01 (meaning 0.01m = 1cm).
 	if !hasCM || mStr != "" {
 		meters, err = strconv.Atoi(mStr)
 		// RFC1876 states the max value is 90000000.00.  The latter two conditions enforce it.

xfr.go

@@ -188,7 +188,7 @@ func (t *Transfer) inIxfr(q *Msg, c chan *Envelope) {
 			if v, ok := rr.(*SOA); ok {
 				if v.Serial == serial {
 					n++
-					// quit if it's a full axfr or the the servers' SOA is repeated the third time
+					// quit if it's a full axfr or the servers' SOA is repeated the third time
 					if axfr && n == 2 || n == 3 {
 						c <- &Envelope{in.Answer, nil}
 						return