title: nodejs & express 4, res.json returns "Content-Type: text/plain"
body: <p>I'm trying to make my application return "application/json" as the content type whenever the response is a json of course. </p>
  
  <p>I have tried:</p>
  
  <pre><code>res.json(jsonContent);
  
  response header has "Content-Type → text/plain; charset=utf-8"
  </code></pre>
  
  <p>and</p>
  
  <pre><code>res.setHeader('content-type', 'text/json');
  res.send(jsonContent); 
  
  response header has "Content-Type → text/plain; charset=utf-8"
  </code></pre>
  
  <p>and </p>
  
  <pre><code>res.set('content-type', 'text/json');
  res.send(jsonContent); 
  
  response header has "Content-Type → text/plain; charset=utf-8"
  </code></pre>
  
  <p>and all of the above at the same time. But my app always server responses as text/plain and never application/json. What might I be doing wrong?</p>