resolve php 8 compatibility

composer.json

@@ -11,7 +11,7 @@
     }
   ],
   "require": {
-    "php": "~5.5.0|~5.6.0|7.0.2|7.0.4|~7.0.6|~7.1.0|~7.2.0|~7.3.0|~7.4.0",
+    "php": "~5.5.0|~5.6.0|7.0.2|7.0.4|~7.0.6|~7.1.0|~7.2.0|~7.3.0|~7.4.0|~8.0.0|~8.1.0",
     "magento/framework": "~100.0|~101.0|~102.0|~103.0",
     "magento/module-customer": "~100.0|~100.1|~100.2|~101.0|~102.0|~103.0"
   },