Fix HighWaterMarks() comment

consumer.go

@@ -63,7 +63,8 @@ type Consumer interface {
 	// or OffsetOldest
 	ConsumePartition(topic string, partition int32, offset int64) (PartitionConsumer, error)
 
-	// HighWaterMarks returns the current high water marks for each topic and partitions
+	// HighWaterMarks returns the current high water marks for each topic and partition
+	// Consistency between partitions is not garanteed since high water marks are updated separately.
 	HighWaterMarks() map[string]map[int32]int64
 
 	// Close shuts down the consumer. It must be called after all child