fix(deps): update dependency rehype-slug to v6 (#20)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

package.json

@@ -53,7 +53,7 @@
     "rehype-parse": "^8.0.4",
     "rehype-raw": "^6.1.1",
     "rehype-rewrite": "^3.0.6",
-    "rehype-slug": "^5.0.1",
+    "rehype-slug": "^6.0.0",
     "remark-gemoji": "^7.0.1",
     "unified": "^10.1.2",
     "unist-util-visit": "^4.1.1",