code: func (db *DB) HIncrBy(key []byte, field []byte, delta int64) (int64, error) {
  	if err := checkHashKFSize(key, field); err != nil {
  		return 0, err
  	}
  
  	t := db.hashBatch
  	var ek []byte
  	var err error
  
  	t.Lock()
  	defer t.Unlock()
  
  	ek = db.hEncodeHashKey(key, field)
  
  	var n int64
  	if n, err = StrInt64(db.bucket.Get(ek)); err != nil {
  		return 0, err
  	}
  
  	n += delta
  
  	_, err = db.hSetItem(key, field, num.FormatInt64ToSlice(n))
  	if err != nil {
  		return 0, err
  	}
  
  	err = t.Commit()
  
  	return n, err
  }
docs: // HIncrBy increases the value of field by delta.