Update custom-server-fastify example to not use internal fn (#11040)

examples/custom-server-fastify/package.json

@@ -7,10 +7,10 @@
     "start": "cross-env NODE_ENV=production node ./server.js"
   },
   "dependencies": {
-    "cross-env": "^5.2.0",
-    "fastify": "2.1.0",
+    "cross-env": "^7.0.2",
+    "fastify": "^2.12.1",
     "next": "latest",
-    "react": "^16.8.4",
-    "react-dom": "^16.8.4"
+    "react": "^16.13.0",
+    "react-dom": "^16.13.0"
   }
 }

examples/custom-server-fastify/server.js

@@ -6,6 +6,7 @@ const dev = process.env.NODE_ENV !== 'production'
 
 fastify.register((fastify, opts, next) => {
   const app = Next({ dev })
+  const handle = app.getRequestHandler()
   app
     .prepare()
     .then(() => {
@@ -30,7 +31,7 @@ fastify.register((fastify, opts, next) => {
       })
 
       fastify.all('/*', (req, reply) => {
-        return app.handleRequest(req.req, reply.res).then(() => {
+        return handle(req.req, reply.res).then(() => {
           reply.sent = true
         })
       })