Adding new request for updating transactions in tx-pool

[Mikelle]

Closes https://github.com/hermeznetwork/hermez-node/issues/1035

What does this PR does?

Fixing bug with updating txs in the pool

How to test?

Create a transaction and then update it.

Before fix: After fix:

There is a file from the integration tests run: report.txt

Checklist

These are the criteria that every PR should meet, please check them off as you review them:

• [ ] Include tests
• [x] Respect code style and lint
• [ ] Update swagger file (if needed)
• [ ] Update documentation (*.md) (if needed)