title: Update vsts-npm-auth with new username and password
body: <p>I have installed the <strong>vsts-npm-auth</strong> package using following command:</p>
  
  <pre><code>npm install -g vsts-npm-auth --registry https://registry.npmjs.com
  </code></pre>
  
  <p>And I ran <strong>vsts-npm-auth -config .npmrc</strong> command to set the credential but I am facing below error:</p>
  
  <p><a href="https://i.stack.imgur.com/0f5cD.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/0f5cD.png" alt="enter image description here"></a></p>
  
  <p>Now I need to update the credential but it always fetches the existing credential. Is there any way to send <strong>PUT</strong> request and update the credential ?</p>