Update rubocop requirement from ~> 1.56.3 to ~> 1.57.0 (#43)

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@v1.56.3...v1.57.0)

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

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

Gemfile

@@ -9,7 +9,7 @@ group :developmend do
   gem 'bump', '~> 0.10.0'
   gem 'rake'
   gem 'rspec', '~> 3.12.0'
-  gem 'rubocop', '~> 1.56.3'
+  gem 'rubocop', '~> 1.57.0'
   gem 'simplecov', '~> 0.22.0'
   gem 'simplecov-cobertura', '~> 2.1.0'
 end