makeApproveTx method
Implementation
Future<Transaction> makeApproveTx(Address owner, Address spender,
BigInt amount, int gasPrice, int gasLimit, Address payer) async {
var fn = 'approve';
var b = TxBuilder();
return b.makeInvokeTx(fn, [owner, spender, amount], contract,
gasPrice: gasPrice, gasLimit: gasLimit, payer: payer);
}