在用composer安装Yii2的扩展插件时，报错：
[UnexpectedValueException]
Could not parse version constraint <=2.*: Invalid version string "2.*"
先执行composer self-update
然后执行composer update或composer global update在用composer安装Yii2的扩展插件时，报错：
[UnexpectedValueException]
Could not parse version constraint <=2.*: Invalid version string "2.*"
先执行composer self-update
然后执行composer update或composer global update