Update rubocop requirement from ~> 1.30.1 to ~> 1.31.0 (#199)

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@v1.30.1...v1.31.0)

---
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>

Gemfile

@@ -16,7 +16,7 @@ group(:development) do
   gem('steep', '~> 1.0.1', require: false)
   gem('benchmark-ips', '~> 2.10.0', require: false)
   gem('yard', '~> 0.9.28', require: false)
-  gem('rubocop', '~> 1.30.1', require: false)
+  gem('rubocop', '~> 1.31.0', require: false)
   gem('rubocop-rake', '~> 0.6.0', require: false)
   gem('rubocop-performance', '~> 1.14.2', require: false)
   gem('rubocop-rubycw', '~> 0.1.6', require: false)