Replace deprecated visibility_required rule with modifier_keywords

Author: natanfelles

src/Config.php

@@ -298,7 +298,7 @@ protected function prepareRules() : void
             'type_declaration_spaces' => ['elements' => ['function', 'property']],
             'types_spaces' => ['space' => 'single'],
             'unary_operator_spaces' => true,
-            'visibility_required' => true,
+            'modifier_keywords' => true,
             'void_return' => true,
             'whitespace_after_comma_in_array' => [
                 'ensure_single_space' => true,