upgrade to Laravel 5.6

Author: bhuvidya

composer.json

@@ -17,7 +17,7 @@
     "homepage": "https://github.com/bhuvidya/laravel-countries",
     "license": "MIT",
     "require": {
-        "illuminate/support": "~5.5.0",
+        "illuminate/support": "^5.5.0",
         "php": ">=7.0.0"
     },
     "autoload": {