build(deps-dev): update minitest-parallel_fork requirement

Updates the requirements on [minitest-parallel_fork](https://github.com/jeremyevans/minitest-parallel_fork) to permit the latest version.
- [Changelog](https://github.com/jeremyevans/minitest-parallel_fork/blob/master/CHANGELOG)
- [Commits](jeremyevans/minitest-parallel_fork@1.3.1...2.0.0)

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

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

Gemfile

@@ -21,7 +21,7 @@ group :development do
 
   # tests
   gem "minitest", "5.20.0"
-  gem "minitest-parallel_fork", "1.3.1"
+  gem "minitest-parallel_fork", "2.0.0"
   gem "ruby_memcheck", "2.2.1"
   gem "rubyzip", "~> 2.3.2"
   gem "simplecov", "= 0.21.2"