git: update for v2.3.0

* sort_string_list(): rename to string_list_sort() (upstream commit
  3383e199)
* update read_tree_recursive callback to pass strbuf as base (upstream
  commit 6a0b0b6d)

Signed-off-by: Christian Hesse <mail@eworm.de>

cgit.c

@@ -603,7 +603,7 @@ static int prepare_repo_cmd(void)
 		free(tmp);
 		return 1;
 	}
-	sort_string_list(&ctx.repo->submodules);
+	string_list_sort(&ctx.repo->submodules);
 	cgit_prepare_repo_env(ctx.repo);
 	choose_readme(ctx.repo);
 	return 0;