Bump version

Author: ssx

composer.json

@@ -4,7 +4,7 @@
     "type": "library",
     "keywords": [ "laravel", "validation", "country" ],
     "require": {
-        "illuminate/contracts": "^5.5|^6.0|^7.0",
+        "illuminate/contracts": "^5.5|^6.0|^7.0|^8.0",
         "league/iso3166": "^2.0"
     },
     "require-dev": {