Bump gatsby-transformer-remark from 2.6.39 to 5.25.1

Bumps [gatsby-transformer-remark](https://github.com/gatsbyjs/gatsby/tree/HEAD/packages/gatsby-transformer-remark) from 2.6.39 to 5.25.1.
- [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)

---
updated-dependencies:
- dependency-name: gatsby-transformer-remark
  dependency-type: direct:production
...

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

Author: dependabot[bot]

package.json

@@ -11,7 +11,7 @@
     "gatsby-plugin-sass": "^2.1.24",
     "gatsby-source-datocms": "^2.1.20",
     "gatsby-source-filesystem": "^2.1.40",
-    "gatsby-transformer-remark": "^2.6.39",
+    "gatsby-transformer-remark": "^5.25.1",
     "node-sass": "^4.11.0",
     "react": "^16.10.2",
     "react-dom": "^16.10.2",