Update composer.json to enable PHP7.3 Support

Author: ulftietze

composer.json

@@ -4,7 +4,7 @@
     "type": "magento2-module",
     "description": "Extended Import Features (ported from AvS_FastSimpleImport)",
     "require": {
-        "php": "~5.5.0|~5.6.0|~7.0.0|~7.1.0|~7.2.0"
+        "php": "~5.5.0|~5.6.0|~7.0.0|~7.1.0|~7.2.0|~7.3.0"
     },
 
     "authors": [