build(deps-dev): update minitest requirement from 5.18.1 to 5.19.0

Updates the requirements on [minitest](https://github.com/minitest/minitest) to permit the latest version.
- [Changelog](https://github.com/minitest/minitest/blob/master/History.rdoc)
- [Commits](minitest/minitest@v5.18.1...v5.19.0)

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

Signed-off-by: dependabot[bot] <[email protected]>

Gemfile

@@ -20,7 +20,7 @@ group :development do
   gem "rexical", "= 1.0.7"
 
   # tests
-  gem "minitest", "5.18.1"
+  gem "minitest", "5.19.0"
   gem "minitest-reporters", "1.6.0"
   gem "ruby_memcheck", "1.3.2"
   gem "rubyzip", "~> 2.3.2"