title: How can i import additional files into server.js using sapper?
body: <p>In my sapper app, i try to import a file into the <code>server.js</code> file like this:</p>
  <pre class="lang-js prettyprint-override"><code>import sirv from 'sirv';
  import polka from 'polka';
  import compression from 'compression';
  import * as sapper from '@sapper/server';
  
  const { PORT, NODE_ENV } = process.env;
  const dev = NODE_ENV === 'development';
  
  const pushController = require('./backend/controllers/push');
  
  polka()
      .use(
          compression({ threshold: 0 }),
          sirv('static', { dev }),
          sapper.middleware()
      )
      .post('/something/route', pushController.subscribe)
      .listen(PORT, err =&gt; {
          if (err) console.log('error', err);
      });
  </code></pre>
  <p>But i always get the Error on console:</p>
  <pre><code>Error: Cannot find module './backend/controllers/push
  </code></pre>
  <p>my root folder looks like this:</p>
  <pre><code> - src
     - backend
       - controllers
         - push.js
  
     - client.js
     - server.js
     - service-worker.js
     - template.html
  </code></pre>
  <p>I am using sapper with the default <code>rollup</code> config. Could the error therefore be related to rollup? How can I fix it?</p>