added support for Laravel 6

Author: daveismynamecom

composer.json

@@ -12,7 +12,7 @@
     "homepage": "https://github.com/daveismyname/laravel-microsoft-graph",
     "keywords": ["Laravel", "MsGraph", "Graph", "Microsoft Graph", "Office365"],
     "require": {
-        "illuminate/support": "~5",
+        "illuminate/support": "5.5.x|5.6.x|5.7.x|5.8.x|6.x",
         "league/oauth2-client": "^1.4",
         "guzzlehttp/guzzle": "^6"
     },