title: How to clear https proxy setting of NPM?
body: <p>How can I clear the previous ssl proxy setting of NPM? 
  well, I search a lot, but all post I got is mainly about how to <code>set</code> proxy in corporate network.</p>
  
  <p>I try to set proxy to nothing:</p>
  
  <pre><code>npm config set http-proxy
  npm config set https-proxy
  </code></pre>
  
  <p>the first command pass yet the second one warn that:</p>
  
  <pre><code>npm WARN invalid config proxy=""
  npm WARN invalid config Must be a full url with 'http://'
  </code></pre>
  
  <p>is the warning neglectable and I have successfully clear the proxy setting?</p>