Add support for PHP 8 (#41)

* #39 Add support for PHP 8

Allow PHP 8 versions

* Fix PHP Version

Author: joskfg

composer.json

@@ -26,7 +26,7 @@
         }
     },
     "require": {
-        "php": "^7.2",
+        "php": "^7.2 || ^8.0",
         "ext-json": "*",
         "guzzlehttp/guzzle": "^6.1 || ^7.0.1",
         "guzzlehttp/psr7": "^1.7 || ^2.0",