bump guzzle version for Laravel 8

Author: Dan Jewett

composer.json

@@ -5,7 +5,7 @@
     "require": {
         "php": ">=5.6.4",
         "laravel/framework": ">=5.4.0",
-        "guzzlehttp/guzzle": "^6.2",
+        "guzzlehttp/guzzle": ">=6.2",
         "microsoft/microsoft-graph": "^1.5"
     },
     "license": "MIT",