Fixed PHP DOM extension is not specified as requirement.

sun · web-flow · commit 64b13db0dd6f · 2020-02-20T11:59:37.000+01:00
diff --git a/composer.json b/composer.json
@@ -26,6 +26,7 @@
     "require": {
         "php": "^5.6|^7.0",
         "ext-curl": "*",
+        "ext-dom": "*",
         "ext-mbstring": "*",
         "composer/ca-bundle": "^1.0"
     },
