PB-512: Update magento/dom dependency

- php 7.1 support no longer needed
- use original library

Author: anthoula

app/code/Magento/PageBuilder/composer.json

@@ -22,7 +22,7 @@
         "magento/module-require-js": "*",
         "magento/module-media-storage": "*",
         "php": "~7.3.0||~7.4.0",
-        "magento/dom": "2.1.7"
+        "phpgt/dom": "2.1.6"
     },
     "suggest": {
         "magento/module-review": "*"