Merge pull request #336 from sun/patch-1

Fixed PHP DOM extension is not specified as requirement.

Author: oscarotero

composer.json

@@ -26,6 +26,7 @@
     "require": {
         "php": "^5.6|^7.0",
         "ext-curl": "*",
+        "ext-dom": "*",
         "ext-mbstring": "*",
         "composer/ca-bundle": "^1.0"
     },