Update voxpupuli-rubocop requirement from ~> 2.8.0 to ~> 3.0.0

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@v2.8.0...v3.0.0)

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

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

ra10ke.gemspec

@@ -26,5 +26,5 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency 'pry', '~> 0.14.2'
   spec.add_development_dependency 'rspec', '~> 3.6'
   spec.add_development_dependency 'simplecov', '~> 0.22.0'
-  spec.add_development_dependency 'voxpupuli-rubocop', '~> 2.8.0'
+  spec.add_development_dependency 'voxpupuli-rubocop', '~> 3.0.0'
 end