build(deps): bump prismjs from 1.20.0 to 1.21.0 in /website (#4125)

Bumps [prismjs](https://github.com/PrismJS/prism) from 1.20.0 to 1.21.0.
- [Release notes](https://github.com/PrismJS/prism/releases)
- [Changelog](https://github.com/PrismJS/prism/blob/master/CHANGELOG.md)
- [Commits](https://github.com/PrismJS/prism/compare/v1.20.0...v1.21.0)

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

website/package.json

@@ -35,7 +35,7 @@
     "lodash": "^4.17.15",
     "moment": "^2.24.0",
     "netlify-cms-app": "^2.11.31",
-    "prismjs": "^1.19.0",
+    "prismjs": "^1.21.0",
     "react": "^16.13.1",
     "react-dom": "^16.13.1",
     "react-github-btn": "^1.1.1",