async list(filters) {
    const { completed } = filters;
    const where = {};
    if (completed !== undefined) {
      where.completed = completed ? 1 : 0;
    }
    const list = await this.Todo.findAll({ where });
    return list;
  }
list all todos

@param {Object} [filters] - filters
@param {Boolean} [filters.completed] - filter `completed`
@return {Array<Todo>} query result