Update rubocop requirement from ~> 1.67.0 to ~> 1.68.0 (#259)

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@v1.67.0...v1.68.0)

---
updated-dependencies:
- dependency-name: rubocop
  dependency-type: direct:development
...

Signed-off-by: dependabot[bot] <[email protected]>
Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

Gemfile

@@ -10,7 +10,7 @@ group :development do
 
   gem 'rake', '>= 13'
   gem 'rspec', '~> 3.13.0'
-  gem 'rubocop', '~> 1.67.0'
+  gem 'rubocop', '~> 1.68.0'
   gem 'rubocop-performance', '~> 1.22.0'
   gem 'rubocop-rake', '~> 0.6.0'
   gem 'rubocop-rspec', '~> 3.2.0'