laravel paypal集成中的Php版本问题

Question

我正在尝试安装paypal包并面临此错误

这就是我的composer.json看起来的样子

"require": {
    "php": ">=5.6.4",
    "doctrine/dbal": "^2.5",
    "gloudemans/shoppingcart": "^2.5",
    "laravel/framework": "5.4.*",
    "laravel/tinker": "~1.0",
    "zizaco/entrust": "5.2.x-dev"
},
"require-dev": {
    "fzaninotto/faker": "~1.4",
    "mockery/mockery": "0.9.*",
    "phpunit/phpunit": "~5.7"
},