Update rubocop requirement from ~> 0.67.2 to ~> 0.68.1

Updates the requirements on [rubocop](https://github.com/rubocop-hq/rubocop) to permit the latest version.
- [Release notes](https://github.com/rubocop-hq/rubocop/releases)
- [Changelog](https://github.com/rubocop-hq/rubocop/blob/master/CHANGELOG.md)
- [Commits](rubocop/rubocop@v0.67.2...v0.68.1)

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

Author: dependabot-support

Gemfile

@@ -19,7 +19,7 @@ group :development, :test do
   gem 'guard-rspec', require: false
   gem 'rspec', require: false
 
-  gem 'rubocop', '~> 0.67.2', require: false unless RUBY_VERSION =~ /^1.8/
+  gem 'rubocop', '~> 0.68.1', require: false unless RUBY_VERSION =~ /^1.8/
   gem 'simplecov', require: false
   gem 'terminal-notifier-guard', require: false