Added PHP7.3 support (#14)

Author: devpatil7

composer.json

@@ -5,7 +5,7 @@
         "sort-packages": true
     },
     "require": {
-        "php": "~7.1.3||~7.2.0",
+        "php": "~7.1.3||~7.2.0||~7.3.0",
         "magento/framework": "^102.0",
         "magento/upward": "^1.0.0"
     },