Add KError = 9

According official page, 9 is unused:
http://search.cpan.org/~sgladkov/Kafka/lib/Kafka.pm

But I met lots of "Unknown error, how did this happen? Error code = 9"
So I Found out:
http://search.cpan.org/~sgladkov/Kafka/lib/Kafka.pm

I think the official page is not up to date.

errors.go

@@ -89,6 +89,7 @@ const (
 	NotLeaderForPartition           KError = 6
 	RequestTimedOut                 KError = 7
 	BrokerNotAvailable              KError = 8
+	ReplicaNotAvailable             KError = 9
 	MessageSizeTooLarge             KError = 10
 	StaleControllerEpochCode        KError = 11
 	OffsetMetadataTooLarge          KError = 12
@@ -121,6 +122,8 @@ func (err KError) Error() string {
 		return "kafka server: Request exceeded the user-specified time limit in the request."
 	case BrokerNotAvailable:
 		return "kafka server: Broker not available. Not a client facing error, we should never receive this!!!"
+	case ReplicaNotAvailable:
+		return "kafka server: Replica not available."
 	case MessageSizeTooLarge:
 		return "kafka server: Message was too large, server rejected it to avoid allocation error."
 	case StaleControllerEpochCode: