Update rubocop requirement from ~> 1.16.0 to ~> 1.56.2

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@v1.16.0...v1.56.2)

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

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

station.gemspec

@@ -85,7 +85,7 @@ Gem::Specification.new do |spec|
   spec.add_runtime_dependency('chartkick', '4.0.5')
   spec.add_runtime_dependency('readingtime', '0.4.0')
 
-  spec.add_development_dependency('rubocop', '~> 1.16.0')
+  spec.add_development_dependency('rubocop', '~> 1.56.2')
   spec.add_development_dependency('rubocop-rails', '~> 2.6')
 
   spec.metadata = {