Fix typo in Appender.AppendHistogram() arg name

Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>

tsdb/chunkenc/chunk.go

@@ -94,7 +94,7 @@ type Appender interface {
 	// The returned bool isRecoded can be used to distinguish between the new Chunk c being a completely new Chunk
 	// or the current Chunk recoded to a new Chunk.
 	// The Appender app that can be used for the next append is always returned.
-	AppendHistogram(prev *HistogramAppender, t int64, h *histogram.Histogram, appendOny bool) (c Chunk, isRecoded bool, app Appender, err error)
+	AppendHistogram(prev *HistogramAppender, t int64, h *histogram.Histogram, appendOnly bool) (c Chunk, isRecoded bool, app Appender, err error)
 	AppendFloatHistogram(prev *FloatHistogramAppender, t int64, h *histogram.FloatHistogram, appendOnly bool) (c Chunk, isRecoded bool, app Appender, err error)
 }