Remove deprecation warning for Module#parents

DEPRECATION WARNING: `Module#parents` has been renamed to
`module_parents`. `parents` is deprecated and will be removed in Rails
6.1. (called from model_name at
../ee/app/models/concerns/custom_model_naming.rb:15)

ee/app/models/concerns/custom_model_naming.rb

@@ -12,7 +12,7 @@ module CustomModelNaming
   class_methods do
     def model_name
       @_model_name ||= begin
-        namespace = self.parents.detect do |n|
+        namespace = self.module_parents.detect do |n|
           n.respond_to?(:use_relative_model_naming?) && n.use_relative_model_naming?
         end
         Name.new(self, namespace)