TransactionMapping fromDTO fails to load transactions

[dgarcia360]

1. Expected behavior and actual behavior.

Using TransactionMapping class we can create Transactions using the DTO format. Once we turn a transaction to DTO, and try to recreate it using TransactionMapping.fromDTO(transaction.toJSON()) we get the following error:

TypeError: Cannot read property 'type' of undefined from \nem2sdk\dist\src\infrastructure\transaction\CreateTransactionFromDTO.js:60:36.

2. Steps to reproduce the problem.

    const transferTransaction = TransferTransaction.create(
        Deadline.create(),
        Address.createFromRawAddress('SAGYCE-QM5SK2-TGFUC5-Z5GZJR-ATKTBS-UQQMMH-KW5B'),
        [NetworkCurrencyMosaic.createRelative(10)],
        PlainMessage.create('hello'),
        NetworkType.MIJIN_TEST
    );
    TransactionMapping.createFromDTO(transferTransaction.toJSON());

[rg911]

Ah. looks like swagger DTO wrapped transactions into a 'transaction' property, haha!