Como criar botão para ir para um site?

site = 'www.xtibia.com'

function init()
  testButton = modules.client_topmenu.addRightGameButton('testButton', tr('Test Button'), '/images/topbuttons/battle', toggle)
end

function terminate()
  testButton:destroy()
end

function toggle()
  os.execute('start '..site)
end

Module
  name: game_test
  description: Tester.
  author: Noninhouh
  website: www.xtibia.com
  autoload: true
  sandboxed: true
  scripts: [ test ]
  @onLoad: init()
  @onUnload: terminate()