Merge branch 'feature/php8_compatibility' into develop

Author: ma4nn

composer.json

@@ -25,10 +25,10 @@
     }
   },
   "require": {
-    "php": "^5.6|^7",
-    "dompdf/dompdf": "^0.8",
+    "php": "^5.6|^7|^8",
+    "dompdf/dompdf": "^0.8|^1.0",
     "setasign/fpdi": "^2.0",
-    "setasign/fpdi-fpdf": "^2"
+    "setasign/fpdf": "^1.8|^2"
   },
   "require-dev": {
     "phpunit/phpunit": "^7",