Update rubocop requirement from ~> 1.39.0 to ~> 1.42.0 in /omnibus

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@v1.39.0...v1.42.0)

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

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

common/dependabot-common.gemspec

@@ -41,7 +41,7 @@ Gem::Specification.new do |spec|
   spec.add_development_dependency "rake", "~> 13"
   spec.add_development_dependency "rspec", "~> 3.8"
   spec.add_development_dependency "rspec-its", "~> 1.2"
-  spec.add_development_dependency "rubocop", "~> 1.39.0"
+  spec.add_development_dependency "rubocop", "~> 1.42.0"
   spec.add_development_dependency "rubocop-performance", "~> 1.15.0"
   spec.add_development_dependency "simplecov", "~> 0.22.0"
   spec.add_development_dependency "simplecov-console", "~> 0.9.1"