Update "Send Native Assets (XLM)" example

[JellosPorsche]

The "Send Native Assets (XLM)" needs to be updated to

1. Use the new TransactionBuilder instead of Transaction.Builder
2. Add Network.UseTestNetwork(); to the example? I get a NoNetworkSelectedException if Network.UseTestNetwork(); isn't present before the transaction.Sign(sourceKeypair); statement.

Thanks for creating and maintaining this library.

[Kirbyrawr]

Hi, thanks for the issue, you are right i should update it to follow the new structure, i will try to do it soon.

Regarding the network, it's just an example of exactly how to send it but maybe you are right and it should be included!