for-each-ref: fix description of '--contains' in manpage

'git for-each-ref's manpage says that '--contains' only lists tags,
but it lists all kinds of refs.
Signed-off-by: NSZEDER Gábor <szeder@ira.uka.de>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

Documentation/git-for-each-ref.txt

@@ -76,7 +76,7 @@ OPTIONS
 	specified commit (HEAD if not specified).
 
 --contains [<object>]::
-	Only list tags which contain the specified commit (HEAD if not
+	Only list refs which contain the specified commit (HEAD if not
 	specified).
 
 FIELD NAMES