Bump up docusaurus theme + downgrade mdx-js/react causing issue with docusaurus config

Signed-off-by: jffarge <jf@dagger.io>

website/package.json

@@ -19,8 +19,8 @@
   },
   "dependencies": {
     "@docusaurus/core": "^2.0.0-beta.15",
-    "@docusaurus/preset-classic": "^2.0.0-beta.14",
-    "@mdx-js/react": "^2.0.0",
+    "@docusaurus/preset-classic": "^2.0.0-beta.15",
+    "@mdx-js/react": "^1.6.22",
     "@svgr/webpack": "^6.2.1",
     "amplitude-js": "^8.16.1",
     "clsx": "^1.1.1",