Update rubocop-performance requirement from ~> 1.19.0 to ~> 1.20.0

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@v1.19.0...v1.20.0)

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

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

Gemfile

@@ -14,7 +14,7 @@ group :development do
   gem 'rspec',                 '~> 3.0'
   gem 'rspec-benchmark',       '~> 0.6.0'
   gem 'rubocop',               '~> 1.59.0'
-  gem 'rubocop-performance',   '~> 1.19.0'
+  gem 'rubocop-performance',   '~> 1.20.0'
   gem 'rubocop-rspec',         '~> 2.25.0'
   gem 'simplecov',             '>= 0.18.0', '< 0.23.0'
   gem 'yard',                  '~> 0.9.5'