code: function isTaskListItemToken(tokens, index) {
      return tokens[index].type === 'inline'
          && tokens[index - 1].type === 'paragraph_open'
          && tokens[index - 2].type === 'list_item_open'
          && (tokens[index].content.indexOf('[ ]') === 0
              || tokens[index].content.indexOf('[x]') === 0
              || tokens[index].content.indexOf('[X]') === 0);
  }
docs: Return boolean value whether task list item or not
  @param {array} tokens Token object
  @param {number} index Number of token index
  @returns {boolean}
  @ignore