PB-416: Phpgt/Dom does not support PHP 7.1.0

 - update composer

Author: cspruiell

app/code/Magento/PageBuilder/composer.json

@@ -22,7 +22,7 @@
         "magento/module-require-js": "*",
         "magento/module-media-storage": "*",
         "php": "~7.1.3||~7.2.0||~7.3.0",
-        "phpgt/dom": "1.1.1"
+        "magento/dom": "2.1.7"
     },
     "suggest": {
         "magento/module-review": "*"