signIng method
Implementation
String signIng(String privateKey) {
// sign tx
var msg = getMessageToSign();
EcdaSignature result = EcdaSignature.signForEth(
dynamicToUint8List(msg), privateKey.toUint8List());
return "${(result.v - 27).toRadixString(16)}&${result.r.toStr()}&${result.s.toStr()}";
}