Revert "Update dependency @mdx-js/react to v2"

This reverts commit df9929c.

Author: Matyrobbrt

docs/package-lock.json

@@ -17,7 +17,7 @@
   "dependencies": {
     "@docusaurus/core": "2.0.0-beta.18",
     "@docusaurus/preset-classic": "2.0.0-beta.18",
-    "@mdx-js/react": "2.1.1",
+    "@mdx-js/react": "^1.6.22",
     "clsx": "^1.1.1",
     "prism-react-renderer": "^1.3.1",
     "react": "^17.0.2",