title: mPDF and bootstrap column on next line
body: <p>I'm currently triyng to use mPDF to print a simple HTML page.
  The page is done using bootstrap and it is very basic. 
  Following the documentation, I can print the pdf but while in HTML everything works perfectly, in the pdf the last column is placed on the next line.</p>
  
  <p>Here is the code I'm currently using:</p>
  
  <pre><code>$mpdf = new mPDF('c');
  $html = '&lt;div class="container"&gt;
      &lt;div class="row"&gt;
          &lt;div class="col-xs-2" style="background-color: palevioletred;"&gt;&lt;strong&gt;A&lt;/strong&gt;&lt;/div&gt;
          &lt;div class="col-xs-4" style="background-color: #808080;"&gt;&lt;strong&gt;B&lt;/strong&gt;&lt;/div&gt;
          &lt;div class="col-xs-6" style="background-color: #008000;"&gt;&lt;strong&gt;C&lt;/strong&gt;&lt;/div&gt;
      &lt;/div&gt;
  &lt;/div&gt;';
  $mpdf-&gt;WriteHTML(file_get_contents('./css/bootstrap.css'), 1);
  $mpdf-&gt;WriteHTML($html, 2);
  $mpdf-&gt;Output();
  </code></pre>
  
  <p>The expected output should be:
  <img src="https://i.stack.imgur.com/NgJG8.png" alt="expected output"></p>
  
  <p>but instead the pdf is like this:
  <img src="https://i.stack.imgur.com/FL0KB.png" alt="enter image description here"></p>
  
  <p>Any idea of why is this happening? Can it be fixed?</p>