voxpupuli-rubocop: Pin to patch version

We do the same on other gems as well. It ensures that we get dependabot
PRs for each new release.

beaker-vmware.gemspec

@@ -22,7 +22,7 @@ Gem::Specification.new do |s|
   s.add_development_dependency 'rake', '~> 13.0', '>= 13.0.6'
   s.add_development_dependency 'rspec', '~> 3.0'
   s.add_development_dependency 'rspec-its', '~> 1.3'
-  s.add_development_dependency 'voxpupuli-rubocop', '~> 2.0'
+  s.add_development_dependency 'voxpupuli-rubocop', '~> 2.6.0'
   # Run time dependencies
   s.add_runtime_dependency 'beaker', '>= 4', '< 6'
   s.add_runtime_dependency 'fission', '~> 0.4'