code: func dbPutVersion(dbTx database.Tx, key []byte, version uint32) error {
  	var serialized [4]byte
  	byteOrder.PutUint32(serialized[:], version)
  	return dbTx.Metadata().Put(key, serialized[:])
  }
docs: // dbPutVersion uses an existing database transaction to update the provided
  // key in the metadata bucket to the given version.  It is primarily used to
  // track versions on entities such as buckets.