在执行 composer update 时，报错
You made a reference to a non-existent script @php artisan package:discover
网上说是 composer 的版本太低，查看了一下当前安装的版本
composer -V
Composer version 1.2.1 2016-09-12 11:27:19
解决方法，升级 composer 版本
composer selfupdate
Updating to version 1.6.3 (stable channel).
Downloading: 100%
Use composer self-update --rollback to return to version 1.2.1