Update TransactionBuilder.js

[grctest]

Addresses issue: #137

When creating a proposal, we were incorrectly formatting nested proposal fee asset id's as "1.3.1.3.0" for example, now it's just the fee asset id which fixes the encountered issue.

[grctest]

@svk31 Hey, do you agree on the solution to this bug? Thanks

[sschiessl-bcp]

Hi there @grctest ,

did you check in the bitshares-ui how this part is used for proposals? Does the ui only send the number without 1.3.? Proposals have been working from there in the past

[grctest]

We could do the following instead? That way the UI wouldn't need to be updated.

const _id= proposal.op[1].fee.asset_id;
proposalFeeAssets.push(`${!_id.includes("1.3.") ? "1.3." : ""}${_id}`);

That way the existing UI component wouldn't need to be updated.