build(deps): bump react-dom from 16.4.1 to 16.4.2 in /docs

Bumps [react-dom](https://github.com/facebook/react/tree/HEAD/packages/react-dom) from 16.4.1 to 16.4.2.
- [Release notes](https://github.com/facebook/react/releases)
- [Changelog](https://github.com/facebook/react/blob/master/CHANGELOG.md)
- [Commits](https://github.com/facebook/react/commits/v16.4.2/packages/react-dom)

Signed-off-by: dependabot[bot] <support@github.com>

Author: dependabot[bot]