Update rubocop requirement from ~> 1.24.0 to ~> 1.28.2 (#542)

Updates the requirements on [rubocop](https://github.com/rubocop/rubocop) to permit the latest version.
- [Release notes](https://github.com/rubocop/rubocop/releases)
- [Changelog](https://github.com/rubocop/rubocop/blob/master/CHANGELOG.md)
- [Commits](rubocop/rubocop@v1.24.0...v1.28.2)

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

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>
Co-authored-by: Luke Hill <[email protected]>

cucumber-rails.gemspec

@@ -37,7 +37,7 @@ Gem::Specification.new do |s|
   s.add_development_dependency('database_cleaner', ['>= 1.8', '< 3.0'])
   s.add_development_dependency('rake', '>= 12.0')
   s.add_development_dependency('rspec', '~> 3.6')
-  s.add_development_dependency('rubocop', '~> 1.24.0')
+  s.add_development_dependency('rubocop', '~> 1.28.2')
   s.add_development_dependency('rubocop-packaging', '~> 0.5.1')
   s.add_development_dependency('rubocop-performance', '~> 1.13.3')
   s.add_development_dependency('rubocop-rspec', '~> 2.2.0')