Update RuboCop to 1.13 (#35136).

git-svn-id: http://svn.redmine.org/redmine/trunk@20954 e93f8b46-1217-0410-a6f0-8f06a7374b81

Gemfile

@@ -92,7 +92,7 @@ group :test do
   gem "selenium-webdriver"
   gem 'webdrivers', '~> 4.4', require: false
   # RuboCop
-  gem 'rubocop', '~> 1.12.0'
+  gem 'rubocop', '~> 1.13.0'
   gem 'rubocop-performance', '~> 1.10.1'
   gem 'rubocop-rails', '~> 2.9.0'
 end