chore(website): upgrade docusaurus version to "2.0.0-beta.15"

Author: hasezoey

website/package.json

@@ -10,8 +10,8 @@
     "clear": "docusaurus clear"
   },
   "dependencies": {
-    "@docusaurus/core": "2.0.0-beta.14",
-    "@docusaurus/preset-classic": "2.0.0-beta.14",
+    "@docusaurus/core": "2.0.0-beta.15",
+    "@docusaurus/preset-classic": "2.0.0-beta.15",
     "clsx": "^1.1.1",
     "react": "^17.0.2",
     "react-dom": "^17.0.2"