chore(deps-dev): bump eslint-plugin-mdx from 1.8.2 to 1.13.0 in /docs

Bumps [eslint-plugin-mdx](https://github.com/mdx-js/eslint-mdx) from 1.8.2 to 1.13.0.
- [Release notes](https://github.com/mdx-js/eslint-mdx/releases)
- [Changelog](https://github.com/mdx-js/eslint-mdx/blob/master/CHANGELOG.md)
- [Commits](https://github.com/mdx-js/eslint-mdx/compare/v1.8.2...v1.13.0)

Signed-off-by: dependabot[bot] <support@github.com>

docs/package.json

@@ -42,7 +42,7 @@
   "devDependencies": {
     "eslint": "^7.25.0",
     "eslint-config-prettier": "^8.3.0",
-    "eslint-plugin-mdx": "^1.8.2",
+    "eslint-plugin-mdx": "^1.13.0",
     "eslint-plugin-react": "^7.23.2",
     "null-loader": "^3.0.0",
     "prettier": "2.1.2",