reftable: fix a typo

Fix a typo in comments.

Signed-off-by: Andrew Kreimer <algonell@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: algonell

reftable/reader.h

@@ -30,7 +30,7 @@ struct reftable_reader_offsets {
 
 /* The state for reading a reftable file. */
 struct reftable_reader {
-	/* for convience, associate a name with the instance. */
+	/* for convenience, associate a name with the instance. */
 	char *name;
 	struct reftable_block_source source;