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/controllers/debates_controller_spec.rb

@@ -3,11 +3,11 @@ require 'rails_helper'
 describe DebatesController do
 
   describe 'POST create' do
-    before(:each) do
+    before do
       InvisibleCaptcha.timestamp_enabled = false
     end
 
-    after(:each) do
+    after do
       InvisibleCaptcha.timestamp_enabled = true
     end