Update rubocop requirement from ~> 0.88.0 to ~> 0.89.0 (#81)

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@v0.88.0...v0.89.0)

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

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

Author: dependabot-preview[bot]

Gemfile

@@ -14,5 +14,5 @@ group :development, :test do
 end
 
 group :development do
-  gem 'rubocop', '~> 0.88.0', require: false
+  gem 'rubocop', '~> 0.89.0', require: false
 end