Update voxpupuli-rubocop requirement from ~> 2.3.0 to ~> 2.4.0

Updates the requirements on [voxpupuli-rubocop](https://github.com/voxpupuli/voxpupuli-rubocop) to permit the latest version.
- [Changelog](https://github.com/voxpupuli/voxpupuli-rubocop/blob/master/CHANGELOG.md)
- [Commits](voxpupuli/voxpupuli-rubocop@v2.3.0...v2.4.0)

---
updated-dependencies:
- dependency-name: voxpupuli-rubocop
  dependency-type: direct:development
...

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

puppet-ghostbuster.gemspec

@@ -23,7 +23,7 @@ Gem::Specification.new do |s|
   s.add_development_dependency 'rspec', '~> 3.0'
   s.add_development_dependency 'rspec-collection_matchers', '~> 1.0'
   s.add_development_dependency 'rspec-its', '~> 1.0'
-  s.add_development_dependency 'voxpupuli-rubocop', '~> 2.3.0'
+  s.add_development_dependency 'voxpupuli-rubocop', '~> 2.4.0'
   s.add_runtime_dependency 'json', '>= 2.0', '< 3.0'
   s.add_runtime_dependency 'puppet', '>= 6.0', '< 9.0'
   s.add_dependency         'puppet-lint', '>= 1.0', '< 5.0'