Update Rake 13 for development to suppress a warning

This PR updates Rake to version 13 to suppress the following warning:

```console
$ bundle exec rake
(snip)

/Users/koic/.rbenv/versions/3.4.1/lib/ruby/gems/3.4.0/gems/rake-12.3.3/lib/rake.rb:33:
warning: ostruct was loaded from the standard library,
but will no longer be part of the default gems starting from Ruby 3.5.0.
You can add ostruct to your Gemfile or gemspec to silence this warning.
```

Gemfile

@@ -3,5 +3,5 @@ source "https://rubygems.org"
 # Specify your gem's dependencies in rubocop-rubycw.gemspec
 gemspec
 
-gem "rake", "~> 12.0"
+gem "rake", "~> 13.0"
 gem 'rspec'