chore(deps): update rubocop requirement from ~> 1.57.0 to ~> 1.64.1

Updates the requirements on [rubocop](https://github.com/rubocop/rubocop) to permit the latest version.
- [Release notes](https://github.com/rubocop/rubocop/releases)
- [Changelog](https://github.com/rubocop/rubocop/blob/master/CHANGELOG.md)
- [Commits](rubocop/rubocop@v1.57.0...v1.64.1)

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

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

graphql-client.gemspec

@@ -18,7 +18,7 @@ Gem::Specification.new do |s|
   s.add_development_dependency "minitest", "~> 5.9"
   s.add_development_dependency "rake", "~> 13.1.0"
   s.add_development_dependency "rubocop-github"
-  s.add_development_dependency "rubocop", "~> 1.57.0"
+  s.add_development_dependency "rubocop", "~> 1.64.1"
 
   s.required_ruby_version = ">= 2.1.0"