源码直接下载后运行就提示Composer detected issues in your platform: Your Composer dependencies require a PHP version ">= 7.1.3".

2.x源码直接下载后运行就提示Composer detected issues in your platform: Your Composer dependencies require a PHP version ">= 7.1.3".
文档中不是说明php版本大于5.3.3就可以了吗，我用5.6都不行，用网上的方法：将根目录中的composer.json添加
```
"config": {
    "platform-check": false
}
```
在根目录下 composer dump 浏览器访问直接报错