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] <[email protected]>

facterdb.gemspec

@@ -21,7 +21,7 @@ Gem::Specification.new do |s|
   s.add_development_dependency 'rake', '~> 13.2', '>= 13.2.1'
   s.add_development_dependency 'rspec', '~> 3.13'
 
-  s.add_development_dependency 'voxpupuli-rubocop', '~> 2.8.0'
+  s.add_development_dependency 'voxpupuli-rubocop', '~> 3.0.0'
   s.add_runtime_dependency 'facter', '< 5.0.0'
   s.add_runtime_dependency 'jgrep', '~> 1.5', '>= 1.5.4'
 end