convert src/pages/404.js to Reason

[Peter Piekarczyk]

it's such an easy one 😄

https://github.com/draftbit/avatar-generator/blob/master/src/pages/404.js

import React from 'react'
import Layout from '../components/layout'

const NotFoundPage = () => (
  <Layout>
    <h1>NOT FOUND</h1>
    <p>You just hit a route that doesn&#39;t exist... the sadness.</p>
  </Layout>
)

export default NotFoundPage