user session logout to send new CSRF token upon logout

sessions_controller.rb

def destroy
    warden.authenticate!(:scope => resource_name, :recall => "#{controller_path}#failure")
    current_user.update_column(:authentication_token, nil)
    sign_out
    render :status => 200,
           :json => { :success => true,
                      :info => "Logged out",
                      :csrfParam => request_forgery_protection_token,
                      :csrfToken => form_authenticity_token

           }
end