Bump gatsby from 2.27.4 to 2.28.0

Bumps [gatsby](https://github.com/gatsbyjs/gatsby) from 2.27.4 to 2.28.0.
- [Release notes](https://github.com/gatsbyjs/gatsby/releases)
- [Changelog](https://github.com/gatsbyjs/gatsby/blob/master/CHANGELOG.md)
- [Commits](https://github.com/gatsbyjs/gatsby/compare/[email protected]@2.28.0)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]