chore(rubocop): replace deprecated rspec-focused by rubocop-rspec

WARNING: We are no longer maintaining this gem, and will eventually
archive this repo. We recommend you use rubocop-rspec instead.

https://github.com/CarooDev/rubocop-rspec-focused

Gemfile

@@ -113,7 +113,7 @@ group :development do
   gem 'rubocop', require: false
   gem 'rubocop-performance', require: false
   gem 'rubocop-rails', require: false
-  gem 'rubocop-rspec-focused', require: false
+  gem 'rubocop-rspec', require: false
   gem 'scss_lint', require: false
   gem 'web-console'
 end