rev-list-options.txt: remove reference to --show-notes

In ab18b2c0df ("log/pretty-options: Document --[no-]notes and deprecate
old notes options", 2011-03-30), the `--show-notes` option was
deprecated. However, this reference to it still remains. Change it to
reference the replacement option: `--notes`.

Signed-off-by: Denton Liu <liu.denton@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/rev-list-options.txt

@@ -58,7 +58,7 @@ endif::git-rev-list[]
 	`--all-match`).
 ifndef::git-rev-list[]
 +
-When `--show-notes` is in effect, the message from the notes is
+When `--notes` is in effect, the message from the notes is
 matched as if it were part of the log message.
 endif::git-rev-list[]