Update rubocop-rails requirement from ~> 2.25.0 to ~> 2.28.0

Updates the requirements on [rubocop-rails](https://github.com/rubocop/rubocop-rails) to permit the latest version.
- [Release notes](https://github.com/rubocop/rubocop-rails/releases)
- [Changelog](https://github.com/rubocop/rubocop-rails/blob/master/CHANGELOG.md)
- [Commits](rubocop/rubocop-rails@v2.25.0...v2.28.0)

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

Signed-off-by: dependabot[bot] <[email protected]>

oxidized-web.gemspec

@@ -38,7 +38,7 @@ Gem::Specification.new do |s|
   s.add_development_dependency 'rake',                 '~> 13.0'
   s.add_development_dependency 'rubocop',              '~> 1.64.1'
   s.add_development_dependency 'rubocop-minitest',     '~> 0.35.0'
-  s.add_development_dependency 'rubocop-rails',        '~> 2.25.0'
+  s.add_development_dependency 'rubocop-rails',        '~> 2.28.0'
   s.add_development_dependency 'rubocop-rake',         '~> 0.6.0'
   s.add_development_dependency 'simplecov',            '~> 0.22.0'
   s.add_development_dependency 'simplecov-cobertura',  '~> 2.1.0'