Update rubocop-performance requirement from = 1.16.0 to 1.21.0

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@v1.16.0...v1.21.0)

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

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

Author: dependabot[bot]

Gemfile

@@ -31,7 +31,7 @@ group :development do
   gem "simplecov-console", '~> 0.9',             require: false
   gem "puppet-debugger", '~> 1.0',               require: false
   gem "rubocop", '~> 1.50.0',                    require: false
-  gem "rubocop-performance", '= 1.16.0',         require: false
+  gem "rubocop-performance", '1.21.0',         require: false
   gem "rubocop-rspec", '= 2.19.0',               require: false
   gem "rb-readline", '= 0.5.5',                  require: false, platforms: [:mswin, :mingw, :x64_mingw]
 end