chore: 📌 Support Guzzle v6

Fixes #FAC-1

Author: maicol07

composer.json

@@ -32,7 +32,7 @@
     "license": "MIT",
     "name": "maicol07/flarum-api-client",
     "require": {
-        "guzzlehttp/guzzle": "^7",
+        "guzzlehttp/guzzle": "^6|^7",
         "illuminate/cache": "^6|^7|^8",
         "illuminate/support": "^6|^7|^8",
         "php": ">=7.2",