Update rubocop-performance requirement from 1.21.0 to 1.21.1 (#18)

Updates the requirements on [rubocop-performance](https://github.com/rubocop/rubocop-performance) to permit the latest version.
- [Release notes](https://github.com/rubocop/rubocop-performance/releases)
- [Changelog](https://github.com/rubocop/rubocop-performance/blob/master/CHANGELOG.md)
- [Commits](rubocop/rubocop-performance@v1.21.0...v1.21.1)

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

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

Gemfile

@@ -9,7 +9,7 @@ gem "rake", "~> 13.0"
 gem "rubocop", "1.64.1"
 gem "rubocop-minitest", "0.35.0"
 gem "rubocop-packaging", "0.5.2"
-gem "rubocop-performance", "1.21.0"
+gem "rubocop-performance", "1.21.1"
 gem "rubocop-rake", "0.6.0"
 gem "simplecov", require: false, group: :test
 gem "simplecov_json_formatter", group: :test