title: composer update class phar not found
body: <p>my <a href="/questions/tagged/php" class="post-tag" title="show questions tagged &#39;php&#39;" rel="tag">php</a> version is 7.1.1</p>
  
  <p>i'm trying this code to install react/zmq:</p>
  
  <pre><code>$ composer require react/zmq
  </code></pre>
  
  <p>but i saw this error:</p>
  
  <pre><code> PHP Fatal error:  Uncaught Error: Class 'Phar' not found in /cygdrive/c/ProgramData/ComposerSetup/bin/composer.phar:23
  Stack trace:
  #0 {main}
    thrown in /cygdrive/c/ProgramData/ComposerSetup/bin/composer.phar on line 23
  </code></pre>
  
  <p>what's the problem?</p>