pagination in listIssueComments

I need to fetch all comments (>50) in an issue, but I don't know how to pass params like
```js
{
per_page: 100,
page: 2
}
```
to [`listIssueComments`](https://github.com/michael/github/blob/master/lib/Issue.js#L65).

I also find that there is a method called `_requestAllPages`, but only applied to [`listIssues`](https://github.com/michael/github/blob/master/lib/Issue.js#L43).

Is is better to add options params or use `_requestAllPages` in `listIssueComments`?

Thanks a lot.

先閱讀 lib/Issue.js 中的 listIssues、listIssueComments 和 _requestAllPages，以了解現有的分頁進入點。檢查 listIssueComments 的呼叫方式及文件，然後為呼叫方定義一致的方式來取得多個評論頁面，並確認透過公開 API 可以清楚了解其行為。

由索引模型根據 Issue 內容生成。