code: function update (state, prefix, objectsOrIds, change) {
    if (typeof objectsOrIds !== 'object' && !change) {
      return Promise.reject(
        new Error('Must provide change')
      )
    }
  
    return Array.isArray(objectsOrIds)
      ? updateMany(state, objectsOrIds, change, prefix)
      : updateOne(state, objectsOrIds, change, prefix)
  }
docs: updates existing object.
  
  @param  {String}                   prefix        optional id prefix
  @param  {String|Object|Object[]}   objectsOrIds  id or object (or array of objects) with `._id` property
  @param  {Object|Function}          [change]      Changed properties or function
  that changes existing object
  @return {Promise}