update nextjs-auth0 versionfor auth0 example (#16871)

While running the current [auth0 example](https://github.com/vercel/next.js/tree/canary/examples/auth0), I bumped into this error while trying to access an API route from a page.

```
{
  "error": "_lib_auth0__WEBPACK_IMPORTED_MODULE_1__.default.tokenCache is not a function"
}
```

After checking the [nextjs-auth0](https://github.com/auth0/nextjs-auth0) repo, I realize that they're using version 0.8.0 of the SDK. Changing the package.json to the appropriate version fixes this error.
Signed-off-by: NAdityo Pratomo <pratomo.adityo@gmail.com>

examples/auth0/package.json

@@ -8,7 +8,7 @@
   "author": "",
   "license": "MIT",
   "dependencies": {
-    "@auth0/nextjs-auth0": "^0.6.0",
+    "@auth0/nextjs-auth0": "^0.8.0",
     "next": "latest",
     "react": "^16.12.0",
     "react-dom": "^16.12.0"