安装后，想给nginx升级，为何提示版本不存在。

使用./upgrade.sh，想给nginx升级，为何提示版本不存在。php，redis，mysql都升级成功了。
What Are You Doing?
1. Upgrade Nginx/Tengine
2. Upgrade MySQL/MariaDB/Percona
3. Upgrade PHP
4. Upgrade Redis
5. Upgrade phpMyAdmin
q. Exit
Please input the correct option: 1
Current Nginx Version: 1.9.5
Please input upgrade Nginx Version(example: 1.9.15): 1.9.11
Nginx version does not exist!