Update rubocop requirement from ~> 0.50.0 to ~> 0.67.1

Updates the requirements on [rubocop](https://github.com/rubocop-hq/rubocop) to permit the latest version.
- [Release notes](https://github.com/rubocop-hq/rubocop/releases)
- [Changelog](https://github.com/rubocop-hq/rubocop/blob/master/CHANGELOG.md)
- [Commits](rubocop/rubocop@v0.50.0...v0.67.1)

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

Gemfile

@@ -7,7 +7,7 @@ group :development, :test do
   gem 'fuubar'
   gem 'rake'
   gem 'rspec', '~> 3.0'
-  gem 'rubocop', '~> 0.50.0'
+  gem 'rubocop', '~> 0.67.1'
 end
 
 group :rails do