Allow installation on php8 (#37)

Author: swilla

composer.json

@@ -16,7 +16,7 @@
         }
     ],
     "require": {
-        "php": "^7.1",
+        "php": "^7.1 || ^8.0",
         "guzzlehttp/guzzle": "~6.0 || ~7.0",
         "illuminate/support": "5.7.* || 5.8.* ||^6.0 || ^7.0 || ^8.0",
         "symfony/dotenv": "^4.2 || ^5.1"