Added ext-simplexml dependency to composer.json

Author: Rayne

composer.json

@@ -24,7 +24,8 @@
   "license": "MIT",
   "name": "rayne/wz2008-graph",
   "require": {
-    "php": ">=5.6"
+    "php": ">=5.6",
+    "ext-simplexml": "*"
   },
   "require-dev": {
     "phpunit/phpunit": "^5.0|^7.0",