Use extended CopsDocumentationGenerator

Follow up rubocop/rubocop#13908.

Author: koic

tasks/cops_documentation.rake

@@ -15,9 +15,7 @@ task update_cops_documentation: :yard_for_generate_documentation do
 
   # NOTE: Update `<<next>>` version for docs/modules/ROOT/pages/cops_minitest.adoc
   # when running release tasks.
-  RuboCop::ConfigLoader.inject_defaults!("#{__dir__}/../config/default.yml")
-
-  CopsDocumentationGenerator.new(departments: deps).call
+  CopsDocumentationGenerator.new(departments: deps, plugin_name: 'rubocop-minitest').call
 end
 
 desc 'Syntax check for the documentation comments'