silence deprecation warning from the rename of Module#parent to `Mo…

…dule#module_parent`

Rails 6 deprecated `Module#parent` and friends in rails/rails#34051, replacing them with a `module_*`-prefix naming scheme. This checks to see if `module_parent` is defined, using it if it's available.

lib/rails_erd/domain.rb

@@ -49,7 +49,13 @@ def initialize(models = [], options = {})
     # Returns the domain model name, which is the name of your Rails
     # application or +nil+ outside of Rails.
     def name
-      defined? Rails and Rails.application and Rails.application.class.parent.name
+      return unless defined?(Rails) && Rails.application
+
+      if Rails.application.class.respond_to?(:module_parent)
+        Rails.application.class.module_parent.name
+      else
+        Rails.application.class.parent.name
+      end
     end
 
     # Returns all entities of your domain model.