title: Unable to generate pdf using mpdf in php 7.1
body: <p>i try to generate a simple pdf using mpdf.</p>
  
  <p>This what I used:</p>
  
  <pre><code>1) php 7.1
  2) Laravel 5.3
  3) mpdf dev-master version
  </code></pre>
  
  <p>This is how i write the mpdf code.</p>
  
  <pre><code>    $mpdf = new \Mpdf\Mpdf();
      $mpdf-&gt;WriteHTML('&lt;h1&gt;Hello world!&lt;/h1&gt;');
      $mpdf-&gt;Output("test.pdf", "D");
  </code></pre>
  
  <p>But it will not download and return to me some weird response. But it executed the code successfully.</p>
  
  <p><strong>CHROME</strong>:</p>
  
  <p><a href="https://i.stack.imgur.com/uPbDj.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/uPbDj.png" alt="Chrome error"></a></p>
  
  <p><strong>FIREFOX</strong>: </p>
  
  <p><a href="https://i.stack.imgur.com/8KD3H.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/8KD3H.png" alt="firefox error"></a></p>
  
  <p>Can someone help me? Kind of stuck with this whole day long. </p>