use rubocop-rails

the next version of rubocop 0.72 will remove the rails cops

https://github.com/rubocop-hq/rubocop/blob/master/manual/migrate_rails_cops.md

.rubocop.yml

@@ -6,8 +6,7 @@
 require:
   - ./extras/prohibit_safe_navigation
   - ./extras/prohibit_form_for_and_form_tag
-Rails:
-  Enabled: true
+  - rubocop-rails
 AllCops:
   Include:
     - '**/*.rb'
@@ -111,6 +110,8 @@ Rails/Present:
   UnlessBlank: false
 Rails/SkipsModelValidations:
   Enabled: false
+Rails/HelperInstanceVariable:
+  Enabled: false
 
 # Security
 

Gemfile

@@ -50,6 +50,7 @@ group :test, :development do
   gem "rspec-rails"
   gem "factory_bot_rails"
   gem "rubocop", require: false
+  gem "rubocop-rails", require: false
   gem "rubocop-rspec", require: false
   gem "sqlite3"
   gem "faker"

Gemfile.lock

@@ -195,6 +195,9 @@ GEM
       rainbow (>= 2.2.2, < 4.0)
       ruby-progressbar (~> 1.7)
       unicode-display_width (>= 1.4.0, < 1.7)
+    rubocop-rails (2.0.1)
+      rack (>= 1.1)
+      rubocop (>= 0.70.0)
     rubocop-rspec (1.33.0)
       rubocop (>= 0.60.0)
     ruby-enum (0.7.2)
@@ -267,6 +270,7 @@ DEPENDENCIES
   rqrcode
   rspec-rails
   rubocop
+  rubocop-rails
   rubocop-rspec
   ruumba
   scenic