Update rubocop requirement from ~> 1.12.0 to ~> 1.13.0

Updates the requirements on [rubocop](https://github.com/rubocop/rubocop) to permit the latest version.
- [Release notes](https://github.com/rubocop/rubocop/releases)
- [Changelog](https://github.com/rubocop/rubocop/blob/master/CHANGELOG.md)
- [Commits](rubocop/rubocop@v1.12.0...v1.13.0)

Signed-off-by: dependabot-preview[bot] <support@dependabot.com>

colorls.gemspec

@@ -76,7 +76,7 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency 'ronn', '~> 0'
   spec.add_development_dependency 'rspec', '~> 3.7'
   spec.add_development_dependency 'rspec-its', '~> 1.2'
-  spec.add_development_dependency 'rubocop', '~> 1.12.0'
+  spec.add_development_dependency 'rubocop', '~> 1.13.0'
   spec.add_development_dependency 'rubocop-performance', '~> 1.10.1'
   spec.add_development_dependency 'rubocop-rake', '~> 0.5'
   spec.add_development_dependency 'rubocop-rspec', '~> 2.0'