builtin/grep.c: mark strings for translation

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/grep.c

@@ -489,7 +489,7 @@ static int grep_cache(struct grep_opt *opt, struct repository *repo,
 	}
 
 	if (repo_read_index(repo) < 0)
-		die("index file corrupt");
+		die(_("index file corrupt"));
 
 	for (nr = 0; nr < repo->index->cache_nr; nr++) {
 		const struct cache_entry *ce = repo->index->cache[nr];