Update Guzzle to ~6.3

Author: codyphobe

composer.json

@@ -20,7 +20,7 @@
     "require": {
         "php": ">=7.1.2",
         "ext-json": "*",
-        "guzzlehttp/guzzle": "~6.0",
+        "guzzlehttp/guzzle": "~6.3",
         "illuminate/notifications": "^5.6",
         "illuminate/support": "^5.6",
         "illuminate/queue": "^5.6",