Add missing composer dependency

Author: Omranic

composer.json

@@ -45,7 +45,8 @@
         "illuminate/http": "~5.6.0",
         "illuminate/routing": "~5.6.0",
         "illuminate/support": "~5.6.0",
-        "illuminate/validation": "~5.6.0"
+        "illuminate/validation": "~5.6.0",
+        "watson/validating": "^3.1.0"
     },
     "require-dev": {
         "codedungeon/phpunit-result-printer": "^0.6.0",