Update Mpdf version for PHP 7.4 support

Author: ADmad

README.md

@@ -9,8 +9,8 @@ Plugin containing CakePdf lib which will use a PDF engine to convert HTML to PDF
 
 Engines included in the plugin:
 * DomPdf (^0.8)
-* Mpdf (^7.0)
-* Tcpdf (^6.2)
+* Mpdf (^8.0.4)
+* Tcpdf (^6.3)
 * WkHtmlToPdf **RECOMMENDED ENGINE**
 
 Community maintained engines:

composer.json

@@ -10,7 +10,7 @@
     "require-dev": {
         "phpunit/phpunit": "~8.5.0",
         "dompdf/dompdf": "^0.8",
-        "mpdf/mpdf": "^7.0",
+        "mpdf/mpdf": "^8.0.4",
         "tecnickcom/tcpdf": "^6.3"
     },
     "suggest": {