blame: fix option name in error message

The option name used in blame's UI is `--reverse`.
Signed-off-by: NMax Kirillov <max@max630.net>
Signed-off-by: NJunio C Hamano <gitster@pobox.com>

builtin/blame.c

@@ -2677,7 +2677,7 @@ int cmd_blame(int argc, const char **argv, const char *prefix)
 		sb.commits.compare = compare_commits_by_commit_date;
 	}
 	else if (contents_from)
-		die("--contents and --children do not blend well.");
+		die("--contents and --reverse do not blend well.");
 	else {
 		final_commit_name = prepare_initial(&sb);
 		sb.commits.compare = compare_commits_by_reverse_commit_date;