Add support for Laravel 6 (#37)

Author: dyusha

composer.json

@@ -14,8 +14,8 @@
     "require": {
         "php": ">=7.2",
         "guzzlehttp/guzzle": "^6.2",
-        "illuminate/notifications": "5.5.*|5.6.*|5.7.*|5.8.*",
-        "illuminate/support": "5.5.*|5.6.*|5.7.*|5.8.*"
+        "illuminate/notifications": "5.5.*|5.6.*|5.7.*|5.8.*|^6.0",
+        "illuminate/support": "5.5.*|5.6.*|5.7.*|5.8.*|^6.0"
     },
     "require-dev": {
         "mockery/mockery": "^1.0",