Bump min required enum version from 1.0 to 1.1

Author: marc-mabe

composer.json

@@ -6,7 +6,7 @@
     "license": "BSD-3-Clause",
     "require": {
         "php": "~7.1",
-        "marc-mabe/php-enum": "^1.0 || ^2.0 || ^3.0 || ^4.0",
+        "marc-mabe/php-enum": "^1.1 || ^2.0 || ^3.0 || ^4.0",
         "phpstan/phpstan": "^0.12"
     },
     "require-dev": {