gems: update rubocop-rspec requirement from ~> 2.30.0 to ~> 2.31.0

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@v2.30.0...v2.31.0)

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

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

dyndnsd.gemspec

@@ -44,6 +44,6 @@ Gem::Specification.new do |s|
   s.add_development_dependency 'rspec'
   s.add_development_dependency 'rubocop', '~> 1.64.0'
   s.add_development_dependency 'rubocop-rake', '~> 0.6.0'
-  s.add_development_dependency 'rubocop-rspec', '~> 2.30.0'
+  s.add_development_dependency 'rubocop-rspec', '~> 2.31.0'
   s.add_development_dependency 'solargraph', '~> 0.49.0'
 end