Bump prismjs from 1.25.0 to 1.27.0 in /gatsby (#1278)

Bumps [prismjs](/~https://github.com/PrismJS/prism) from 1.25.0 to 1.27.0.
- [Release notes](/~https://github.com/PrismJS/prism/releases)
- [Changelog](/~https://github.com/PrismJS/prism/blob/master/CHANGELOG.md)
- [Commits](PrismJS/prism@v1.25.0...v1.27.0)

---
updated-dependencies:
- dependency-name: prismjs
  dependency-type: direct:production
...

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

gatsby/package.json

@@ -39,7 +39,7 @@
     "mdx-utils": "^0.1.1",
     "polished": "^3.4.1",
     "prism-react-renderer": "^0.1.7",
-    "prismjs": "^1.25.0",
+    "prismjs": "^1.27.0",
     "prop-types": "^15.7.2",
     "react": "^16.9.0",
     "react-dom": "^16.9.0",