chore(deps): update dependency rubocop to '~> 1.64.0' (#325)

Co-authored-by: renovate[bot] <29139614+renovate[bot]@users.noreply.github.com>

Author: renovate[bot]

Gemfile

@@ -4,6 +4,6 @@ gemspec
 
 group :development, :test do
   # ref: http://docs.rubocop.org/en/latest/installation/
-  gem 'rubocop', '~> 1.63.0', require: false
+  gem 'rubocop', '~> 1.64.0', require: false
   gem 'yard', '~> 0.9.20'
 end