Update rubocop-minitest requirement from ~> 0.12.0 to ~> 0.13.0

Updates the requirements on [rubocop-minitest](https://github.com/rubocop/rubocop-minitest) to permit the latest version.
- [Release notes](https://github.com/rubocop/rubocop-minitest/releases)
- [Changelog](https://github.com/rubocop/rubocop-minitest/blob/master/CHANGELOG.md)
- [Commits](rubocop/rubocop-minitest@v0.12.0...v0.13.0)

---
updated-dependencies:
- dependency-name: rubocop-minitest
  dependency-type: direct:production
...

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

Gemfile

@@ -9,7 +9,7 @@ gem 'inch', require: false # For inline documents
 gem 'minitest', '~> 5.14' # For test
 gem 'rake', '~> 13.0' # For test and automation
 gem 'rubocop', '>= 0.79.0', require: false # For lint
-gem 'rubocop-minitest', '~> 0.12.0', require: false # For lint
+gem 'rubocop-minitest', '~> 0.13.0', require: false # For lint
 gem 'rubocop-performance', '~> 1.11.0', require: false # For lint
 gem 'rubocop-rake', '>= 0.5.1', require: false # For lint
 gem 'rubocop-sensible', '~> 0.3.0', require: false # For lint