使用阿里云的composer镜像，可以极大提高速度。原文详见：https://mirrors.aliyun.com/composer/index.html
composer config -g repo.packagist composer https://mirrors.aliyun.com/composer/ //以上为全局配置
composer config -g --unset repos.packagist//以上为取消配置
删除已经安装过的包
composer remove vendor/package composer update