Update rubocop requirement from ~> 0.74 to ~> 1.8

Updates the requirements on [rubocop](https://github.com/rubocop-hq/rubocop) to permit the latest version.
- [Release notes](https://github.com/rubocop-hq/rubocop/releases)
- [Changelog](https://github.com/rubocop-hq/rubocop/blob/master/CHANGELOG.md)
- [Commits](rubocop/rubocop@v0.74.0...v1.8.0)

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

Gemfile

@@ -6,5 +6,5 @@ source "https://rubygems.org"
 gemspec
 
 gem "coveralls", require: false
-gem "rubocop", "~> 0.74", require: false
+gem "rubocop", "~> 1.8", require: false
 gem "rubocop-rspec", "~> 1.30", require: false