onNext (rawRecord) {
    this._haveRecordStreamed = true
    const record = new Record(this._fieldKeys, rawRecord, this._fieldLookup)
    if (this._observers.some(o => o.onNext)) {
      this._observers.forEach(o => {
        if (o.onNext) {
          o.onNext(record)
        }
      })
    } else {
      this._queuedRecords.push(record)
      if (this._queuedRecords.length > this._highRecordWatermark) {
        this._autoPull = false
      }
    }
  }
Will be called on every record that comes in and transform a raw record
to a Object. If user-provided observer is present, pass transformed record
to it's onNext method, otherwise, push to record que.
@param {Array} rawRecord - An array with the raw record