Update minitest requirement from ~> 5.11.0 to ~> 5.14.2 (#345)

Updates the requirements on [minitest](https://github.com/seattlerb/minitest) to permit the latest version.
- [Release notes](https://github.com/seattlerb/minitest/releases)
- [Changelog](https://github.com/seattlerb/minitest/blob/master/History.rdoc)
- [Commits](minitest/minitest@v5.11.0...v5.14.2)

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

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

Gemfile

@@ -13,6 +13,6 @@ group :development do
 end
 
 group :development, :test do
-  gem 'minitest', '~> 5.11.0'
+  gem 'minitest', '~> 5.14.2'
   gem 'rubocop',  '~> 0.71.0'
 end