在命令行执行composer命令是提示：Warning: This development build of composer is over 60 days old.
报错（报错原因：composer该升级了）：
Warning: This development build of composer is over 60 days old. It is recommended to update it by running "/usr/bin/composer self-update" to get the latest version.
如图：
解决办法（执行下面命令对composer进行升级）：
/usr/bin/composer self-update
升级成功：
