Update rubocop-performance requirement from 1.20.2 to 1.21.0 (#501)

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@v1.20.2...v1.21.0)

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

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

Gemfile

@@ -16,7 +16,7 @@ gem 'overcommit', '0.63.0'
 
 # Pin tool versions (which are executed by Overcommit) for CI builds
 gem 'rubocop', '1.62.1'
-gem 'rubocop-performance', '1.20.2'
+gem 'rubocop-performance', '1.21.0'
 
 gem 'simplecov', '~> 0.22.0'
 gem 'simplecov-lcov', '~> 0.8.0'