Need to add support for `dotFiles` in docsify serve

Can there be an option to allow dot files in `docsify serve`?

E.g. `.prettierrc.yaml`.

i am trying to embed this file, and it is failing:

```md
[.prettierrc.yaml](.prettierrc.yaml ":include")
```

```log
Cannot GET /guides/.prettierrc.yaml
```

## express option to expose:

https://github.com/expressjs/serve-static#dotfiles