Update rubocop requirement from 1.59.0 to 1.60.2 (#133)

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@v1.59.0...v1.60.2)

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

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

Gemfile

@@ -4,7 +4,7 @@ gemspec
 gem "minitest", "~> 5.0"
 gem "minitest-rg", "~> 5.3"
 gem "rake", "~> 13.0"
-gem "rubocop", "1.59.0"
+gem "rubocop", "1.60.2"
 gem "rubocop-minitest", "0.34.5"
 gem "rubocop-packaging", "0.5.2"
 gem "rubocop-rake", "0.6.0"