title: How to set content-type when doing res.send()?
body: <p>At the end of route function, when I do something like this.</p>
  
  <pre><code>res.send(JSON.stringify({...}));
  </code></pre>
  
  <p>I would like the content-type of response to be set as "text/plain", but it is "text/html". Is there way to set it explicitly? I search the document but no clue yet.</p>