Update minitest requirement from ~> 5.18.0 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@v5.18.0...v5.19.0)

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

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

Author: dependabot[bot]

Gemfile

@@ -14,6 +14,6 @@ group :development do
   end
   group :test do
     gem 'rake', '~> 13.0.0'
-    gem 'minitest', '~> 5.18.0'
+    gem 'minitest', '~> 5.19.0'
   end
 end