Explicitely require all rubocop extensions

I think that rspec-rails loaded the other extensions already but Rubocop
was suggesting these extensions to be loaded as well.

The alternative is to disable suggestions of new extensions but that
could hide new shiny tools when they become available.

.rubocop.yml

@@ -5,8 +5,12 @@
 # The configuration is split into three files. Look into those files for more details.
 #
 require:
+  - rubocop-capybara
+  - rubocop-factory_bot
   - rubocop-rails
   - rubocop-rspec
+  - rubocop-rspec_rails
+
 inherit_from:
 
   # The automatically generated todo list to ignore all current violations.