composer 下载失败解决办法

更换composer镜像源，可以执行尝试以下几种：

1、更换成阿里镜像：
composer config -g repo.packagist composer https://mirrors.aliyun.com/composer/

2、更换成Laravel China镜像：
composer config -g repo.packagist composer https://packagist.laravel-china.org

3、更换成中国全量镜像：
composer config -g repo.packagist composer https://packagist.phpcomposer.com