Enable RSpec/HookArgument cop and fix issues

To be consistent about before/after arguments, as `:each` or `:example`
 are same and default scopes, best not to send an argument in those
 scenarios.

Read about cop at http://www.rubydoc.info/gems/rubocop-rspec/RuboCop/Cop/RSpec/HookArgument

spec/rails_helper.rb

@@ -19,7 +19,7 @@ ActiveRecord::Migration.maintain_test_schema!
 
 RSpec.configure do |config|
   config.infer_spec_type_from_file_location!
-  config.after :each do
+  config.after do
     Warden.test_reset!
   end
 end