fix(typo): fix type in async & defer

[JunlinZhu-Tommy]

目标章节：例如 2-ui/05-loading/02-scripts-async-defer

当前上游最新 commit：此处填写本项目英文版 https://github.com/javascript-tutorial/en.javascript.info 的最新 commit，例如 b03ca00

本 PR 所做更改如下：

文件名	参考上游 commit	更改（理由）
article.md	4cf9f5a	修改typo

注意，参考上游 commit 是指你所修改的文件，在英文仓库中同名文件的对应 commit，即你此次提交的修改的依据。如果本 PR 你只是提交一个文字或者语句优化，并非根据上游英文仓库的修改而提交的更新，则请填无。

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[songhn233]

Thanks.

[leviding]

Thanks