title: Call to undefined function Mpdf\mb_regex_encoding()
body: <p>i want to make some reports with yii2 Mpdf but when i running the program i got an error like Call to undefined function Mpdf\mb_regex_encoding() please tell me how to solved this program</p>
  
  <p>this is my controller</p>
  
  <pre><code>public function actionRpt($id)
  {   
      $content = $this-&gt;renderPartial('rpt', [
              'model' =&gt; $this-&gt;findModel($id),
          ]);
  
      // setup kartik\mpdf\Pdf component
      $pdf = new Pdf([
          // set to use core fonts only
          'mode' =&gt; Pdf::MODE_UTF8, 
          // A4 paper format
          'format' =&gt; Pdf::FORMAT_A4, 
          // portrait orientation
          'orientation' =&gt; Pdf::ORIENT_PORTRAIT, 
          // stream to browser inline
          'destination' =&gt; Pdf::DEST_BROWSER, 
          // your html content input
          'content' =&gt; $content,  
          // format content from your own css file if needed or use the
          // enhanced bootstrap css built by Krajee for mPDF formatting 
          'cssFile' =&gt; '@vendor/kartik-v/yii2-mpdf/assets/kv-mpdf-bootstrap.min.css',
          // any css to be embedded if required
          'cssInline' =&gt; '.kv-heading-1{font-size:18px}', 
           // set mPDF properties on the fly
          'options' =&gt; ['title' =&gt; 'RPT NCR'],
           // call mPDF methods on the fly
          'methods' =&gt; [ 
              'SetHeader'=&gt;['NCR'], 
              'SetFooter'=&gt;['{PAGENO}'],
          ]
      ]);
  }
  </code></pre>