最好让composer支持tp6版本

[mfcad]

"require": {
    "topthink/think-installer": "~2.0",
"topthink/framework": "5.1.*",
    "topthink/think-helper": "~1.0",
    "phpunit/phpunit": "^6.0",
    "symfony/dom-crawler": "^2.8.8"
},

现在只支持5.1.*

dev-master 版本的 think-helper 版本是~1.0
但是tp6默认安装的 think-helper版本是 ^3.1