Bump fumadocs-core from 15.8.1 to 15.8.4 in /docs

Bumps [fumadocs-core](https://github.com/fuma-nama/fumadocs) from 15.8.1 to 15.8.4.
- [Release notes](https://github.com/fuma-nama/fumadocs/releases)
- [Commits](https://github.com/fuma-nama/fumadocs/compare/[email protected]@15.8.4)

---
updated-dependencies:
- dependency-name: fumadocs-core
  dependency-version: 15.8.4
  dependency-type: direct:production
  update-type: version-update:semver-patch
...

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

Author: dependabot[bot]

docs/package-lock.json

@@ -9,7 +9,7 @@
     "postinstall": "fumadocs-mdx"
   },
   "dependencies": {
-    "fumadocs-core": "^15.7.13",
+    "fumadocs-core": "^15.8.4",
     "fumadocs-mdx": "^12.0.3",
     "fumadocs-typescript": "^4.0.8",
     "fumadocs-ui": "^15.8.1",