sign method
Signs the transaction for the signer
and given network
passphrase.
Implementation
void sign(KeyPair signer, Network network) {
checkNotNull(signer, "signer cannot be null");
checkNotNull(network, "signer cannot be null");
Uint8List txHash = this.hash(network);
_mSignatures.add(signer.signDecorated(txHash));
}