PHP 8 Support

Author: hailwood

composer.json

@@ -19,7 +19,7 @@
         }
     ],
     "require": {
-        "php": "^7.3",
+        "php": "^7.3|^8.0",
         "xeroapi/xero-php-oauth2": "^2.0",
         "laravel/framework": "^5.5|^6.0|^7.0|^8.0"
     },