Hapi Registration Error

package.json

{
  "scripts": {
    "start": "nodemon server.js",
    "test": "echo \"Error: no test specified\" && exit 1"
  },
  "dependencies": {
    "h2o2": "^5.4.0",
    "hapi": "^16.1.1",
    "joi": "^10.3.4",
    "wreck": "^12.0.0"
  },
  "devDependencies": {
    "eslint": "^3.19.0",
    "eslint-config-hapi": "^10.0.0",
    "eslint-plugin-hapi": "^4.0.0",
    "nodemon": "^1.11.0"
  }
}

server.js

'use strict';

const Hapi = require('hapi');

// Create a server with a host and port
const server = new Hapi.Server();
server.connection({
  host: 'localhost',
  port: process.env.PORT || 8000
});

// Add the route
server.route({
  method: 'GET',
  path: '/hello',
  handler: function (request, reply) {

    return reply('hello world');
  }
});

// Register plugins
server.register(require('joi'), (err) => {

  if (err) {
    throw err;
  }

  // Start the server
  server.start((err) => {

    if (err) {
      throw err;
    }
    console.log('Server running at:', server.info.uri);
  });
});