### Before submitting an issue, please be sure to

- [x] Read [the contributing instructions](https://github.com/github/pages-gem/blob/master/docs/CONTRIBUTING.md#contributing-to-the-github-pages-gem)
- [x] Update to the latest Gem version (run `bundle update github-pages`)

### This issue affects

- [ ] The site generated by GitHub Pages
- [x] Building sites locally

*The GitHub Pages Gem is intended to help users replicate the GitHub Pages build environment locally. If your issue affects both the hosted version and the version previewed locally, you may be better suited reporting [seeking support in other forums](https://github.com/github/pages-gem/blob/master/docs/SUPPORT.md).*

### What did you do (e.g., steps to reproduce)

`index.md`

```md

# Heading

More...

```

### What did you expect to happen?

Jekyll should use the same markdown parser and settings locally as GitHub Pages.

```md

Heading

More…

```

### What happened instead?

Jekyll seems to incorrectly use its own default Kramdown parser instead of GFM CommonMark, and as a result cannot handle Markdown in HTML or smart ellipses.

```md

# Heading

More...

```

### Additional information

* Link to the source repo (if applicable): https://github.com/nickmccurdy/eslint-config-modern/tree/2699a9c01e68535a3a087759cb11e5f82905db88/docs

As a workaround, I guessed at what GitHub's Jekyll config was and ended up using this, which works the same with this example both locally and on GitHub Pages:

```yml
markdown: CommonMarkGhPages
commonmark:
options: ["SMART"]
```

However, I think the gem should replicate this functionality automatically to keep local testing consistent with GitHub. I'm also not sure if I'm missing other options that may differ in both environments.