fixup! Simplify adding a singleton accessor

Author: pirj

lib/rspec/rails/configuration.rb

@@ -67,7 +67,7 @@ def self.initialize_configuration(config) # rubocop:disable Metrics/MethodLength
       config.add_setting :use_transactional_fixtures, alias_with: :use_transactional_examples
       config.add_setting :use_instantiated_fixtures
       config.add_setting :global_fixtures
-      (class << config; self; end).class_exec { attr_accessor :fixture_path }
+      config.singleton_class.class_exec { attr_accessor :fixture_path }
 
       config.include RSpec::Rails::FixtureSupport, :use_fixtures