message: Fixes SignRequest tests
diff: @@ -37,7 +37,7 @@ namespace Hyperledger.Indy.Test.LedgerTests
  {
  var msg = "{\"reqId\":1496822211362017764}";
  - var ex = await Assert.ThrowsExceptionAsync<WalletValueNotFoundException>(() =>
  + var ex = await Assert.ThrowsExceptionAsync<WalletItemNotFoundException>(() =>
  Ledger.SignRequestAsync(wallet, DID1, msg)
  );
  