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/customization_engine_spec.rb

@@ -21,7 +21,7 @@ describe 'Customization Engine' do
     expect(test_key).to eq 'Not overriden string with custom locales'
   end
 
-  after(:each) do
+  after do
     I18n.load_path = default_path
     I18n.reload!
   end