Update rubocop-rspec requirement from ~> 2.26 to >= 2.26, < 4.0

Updates the requirements on [rubocop-rspec](https://github.com/rubocop/rubocop-rspec) to permit the latest version.
- [Release notes](https://github.com/rubocop/rubocop-rspec/releases)
- [Changelog](https://github.com/rubocop/rubocop-rspec/blob/master/CHANGELOG.md)
- [Commits](rubocop/rubocop-rspec@v2.26.0...v3.0.0)

---
updated-dependencies:
- dependency-name: rubocop-rspec
  dependency-type: direct:production
...

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

voxpupuli-rubocop.gemspec

@@ -18,5 +18,5 @@ Gem::Specification.new do |s|
   s.add_runtime_dependency 'rubocop-minitest', '~> 0.35.0'
   s.add_runtime_dependency 'rubocop-performance', '~> 1.21.0'
   s.add_runtime_dependency 'rubocop-rake', '~> 0.6.0'
-  s.add_runtime_dependency 'rubocop-rspec', '~> 2.26'
+  s.add_runtime_dependency 'rubocop-rspec', '>= 2.26', '< 4.0'
 end