gems: update rubocop-rspec requirement from ~> 3.7.0 to ~> 3.8.0

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](https://github.com/rubocop/rubocop-rspec/compare/v3.7.0...v3.8.0)

---
updated-dependencies:
- dependency-name: rubocop-rspec
  dependency-version: 3.8.0
  dependency-type: direct:development
...

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

openvpn-status-web.gemspec

@@ -40,6 +40,6 @@ Gem::Specification.new do |s|
   s.add_development_dependency 'rspec'
   s.add_development_dependency 'rubocop', '~> 1.81.1'
   s.add_development_dependency 'rubocop-rake', '~> 0.7.1'
-  s.add_development_dependency 'rubocop-rspec', '~> 3.7.0'
+  s.add_development_dependency 'rubocop-rspec', '~> 3.8.0'
   s.add_development_dependency 'solargraph', '~> 0.50.0'
 end