Composer更改镜像地址为中国镜像，提高下载速度
查看Composer配置中的镜像地址：
composer config -gl
修改镜像地址为中国镜像：
composer config -g repo.packagist composer https://packagist.phpcomposer.com
再次查看：
其他镜像选择：
#阿里云
composer config -g repo.packagist composer https://mirrors.aliyun.com/composer/
#腾讯云
composer config -g repo.packagist composer https://mirrors.cloud.tencent.com/composer/
