Update rubocop requirement from ~> 1.60.2 to ~> 1.75.8

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@v1.60.2...v1.75.8)

---
updated-dependencies:
- dependency-name: rubocop
  dependency-version: 1.75.8
  dependency-type: direct:production
...

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

Author: dependabot[bot]

Gemfile

@@ -9,5 +9,5 @@ gem "codeclimate-test-reporter", "0.4.4"
 gem "pry"
 gem "rake"
 gem "rspec", "~> 3.1"
-gem "rubocop", "~> 1.60.2"
+gem "rubocop", "~> 1.75.8"
 gem "simplecov", "!= 0.18.0", "!= 0.18.1", "!= 0.18.2", "!= 0.18.3", "!= 0.18.4", "!= 0.18.5", "!= 0.19.0", "!= 0.19.1"