引入 sdk.js 的 script 标签不能用defer属性？

加入`defer`属性后提示：`amisRequire is not defined`。

代码是官网的示例：

```

(function () {
let amis = amisRequire('amis/embed');
// 通过替换下面这个配置来生成不同页面
let amisJSON = {
type: 'page',
title: '表单页面',
body: {
type: 'form',
mode: 'horizontal',
api: '/saveForm',
body: [
{
label: 'Name',
type: 'input-text',
name: 'name'
},
{
label: 'Email',
type: 'input-email',
name: 'email'
}
]
}
};
let amisScoped = amis.embed('#root', amisJSON);
})();

```

Start with the reported sdk.js example and compare how the two deferred script tags are loaded. Verify the behavior in a browser, focusing on when amisRequire becomes available; done means the example runs with defer on both tags without an "amisRequire is not defined" error.

Written by the indexing model from the issue text.