title: Install package on non-empty folder using composer
body: <p>I tried to install package via composer but it's keep telling me that this directory is not empty so how can I install package on non-empty folder using composer ? is there force install command ?</p>
  
  <p>error message:</p>
  
  <pre><code>  [InvalidArgumentException]
    Project directory Yii-GZero-2b/ is not empty.
  </code></pre>