Fatal error: Call-time pass-by-reference has been removed functions/functions_lookups

Hello,i building my old site program(lightinthebox),and i have do some thing for it,then it work fine with admin page,but display error with index,so i try to find ful help from here.
Thanks
Fatal error: Call-time pass-by-reference has been removed in /home/getappreal/public_html/shop/includes/functions/functions_lookups.php on line 51
here is my host info:
Server Information

Server Host: shop.targetmarts Database Host: localhost (127.0.0.1)
Server OS: Linux 2.6.32-773.26.1.lve1.4.46.el6.x86_64 Database: MySQL 5.6.36-cll-lve
Server Date: 03/03/2018 11:28:37 Database Date: 03/03/2018 11:28:37
Server Up Time: 11:28:37 up 34 days, 21:06, 0 users, load average: 5.33, 5.68, 5.92 HTTP Server: Apache
PHP Version: 5.6.32 (Zend: 2.6.0) PHP Memory Limit: 128M PHP Safe Mode: Off
PHP File Uploads: On Max Size: 2M POST Max Size: 8M
Database Data Size: 7,707 kB Database Index Size: 1,373 kB

functions_lookups.php on line 51 :

      array_unshift(&$countries_array,array('countries_id' => '-1','countries_name' => '-----------------------'));

The problem is you are using zen cart 1.3.8 on php 5.6. That will not work.

Design75:

The problem is you are using zen cart 1.3.8 on php 5.6. That will not work.

But the admin page work fine,so i think you can help me to fix this.
Thanks

The line 51 you gave is not in the original 1.3.8a file. Can you post +/- 10 lines counting from line 51?
Bets advice is to upgrade the zen Cart 1.5.5f. You version is mor then 10 years old.