Update composer.json

Author: repat

composer.json

@@ -4,7 +4,7 @@
     "type": "library",
     "keywords": [ "laravel", "validation", "colour" ],
     "require": {
-        "illuminate/contracts": "^5.5"
+        "illuminate/contracts": "^5.5 | ^6.0"
     },
     "require-dev": {
         "orchestra/testbench": "^3.5",