Add Guzzle 7 support

Author: halloei

composer.json

@@ -21,7 +21,7 @@
     "require": {
         "php": ">=7.1",
         "ext-json": "*",
-        "guzzlehttp/guzzle": "^6.2",
+        "guzzlehttp/guzzle": "^6.2 || ^7.0",
         "illuminate/notifications": "^5.5 || ^6.0 || ^7.0",
         "illuminate/support": "^5.5 || ^6.0 || ^7.0"
     },