Update rubocop requirement from ~> 1.80.0 to ~> 1.81.0 (#141)

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@v1.80.0...v1.81.0)

---
updated-dependencies:
- dependency-name: rubocop
  dependency-version: 1.81.0
  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

@@ -8,7 +8,7 @@ group :development do
   gem 'minitest', '~> 5.25.0'
   gem 'minitest-around', '~> 0.5.0'
   gem 'rake', '>= 10.0.0'
-  gem 'rubocop', '~> 1.80.0'
+  gem 'rubocop', '~> 1.81.0'
   gem 'rubocop-minitest', '~> 0.38.0'
   gem 'rubocop-performance', '~> 1.26.0'
   gem 'rubocop-rake', '~> 0.7.1'