Downgrade docusaurus

Version 2.0.1 breaks the github actions deploy. Based on the issue
below, docusaurus was working on 2.0.0-rc.1. This commit downgrades
docusuarus to the latter version.

See: facebook/docusaurus#7744

docs/package.json

@@ -15,9 +15,9 @@
     "write-heading-ids": "docusaurus write-heading-ids"
   },
   "dependencies": {
-    "@docusaurus/core": "latest",
-    "@docusaurus/plugin-content-docs": "latest",
-    "@docusaurus/preset-classic": "latest",
+    "@docusaurus/core": "2.0.0-rc.1",
+    "@docusaurus/plugin-content-docs": "2.0.0-rc.1",
+    "@docusaurus/preset-classic": "2.0.0-rc.1",
     "@mdx-js/react": "^1.6.21",
     "clsx": "^1.1.1",
     "docusaurus2-dotenv": "^1.4.0",