How to use the puregram.Keyboard.keyboard function in puregram

telegram.updates.hear('/keyboard', (context) => {
  return context.send('There\'s your keyboard!', {
    reply_markup: Keyboard.keyboard([
      [
        Keyboard.textButton('Button'),
      ],

      [
        Keyboard.textButton('Another button'),
        Keyboard.textButton('But there\'s more!'),
      ],

      [
        Keyboard.textButton('So'),
        Keyboard.textButton('many'),
        Keyboard.textButton('buttons!'),
      ],
    ]).resize(),
  });