title: composer installation from behind proxy server
body: <p>I'm trying to run <code>composer update</code> on windows 10 behind a proxy server, it gives me an error.
  <a href="https://i.stack.imgur.com/UyFkw.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/UyFkw.png" alt="enter image description here"></a></p>
  
  <p>and I set http proxy using below command</p>
  
  <pre><code>SET HTTP_PROXY="http://192.168.1.6:808"
  SET HTTPS_PROXY="http://192.168.1.6:808"
  </code></pre>
  
  <p>this also return same error.</p>