全局安装
下载composer.phar文件
curl -sS https://getcomposer.org/installer | php
如果报错，通过下面方式
php -r "readfile('https://getcomposer.org/installer');" | php
mv composer.phar /usr/local/bin/composer
使用国内镜像
composer config -g repo.packagist composer https://packagist.phpcomposer.com