build(deps): bump gatsby-transformer-remark in /docs (#1300)

Bumps [gatsby-transformer-remark](https://github.com/gatsbyjs/gatsby/tree/HEAD/packages/gatsby-transformer-remark) from 2.8.27 to 2.8.28.
- [Release notes](https://github.com/gatsbyjs/gatsby/releases)
- [Changelog](https://github.com/gatsbyjs/gatsby/blob/master/packages/gatsby-transformer-remark/CHANGELOG.md)
- [Commits](https://github.com/gatsbyjs/gatsby/commits/[email protected]/packages/gatsby-transformer-remark)

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

docs/package-lock.json

@@ -35,7 +35,7 @@
     "gatsby-remark-mermaid": "^2.0.0",
     "gatsby-remark-responsive-iframe": "^2.4.12",
     "gatsby-source-filesystem": "^2.3.23",
-    "gatsby-transformer-remark": "^2.8.27",
+    "gatsby-transformer-remark": "^2.8.28",
     "gatsby-transformer-sharp": "^2.5.12",
     "gatsby-transformer-yaml": "^2.4.10",
     "polished": "^3.6.5",