[ecash-herald] Parse iceberg lowercase

Summary:
IceBerg is probably a solo miner using CK pool software. So, we don't want to parse as 'CK Pool, mined by iceberg'

Recently IceBerg is going by iceberg. Catch this.

It's prob the same as IceBerg but if he's iceberg now, his call

Test Plan: npm test

Reviewers: #bitcoin_abc, Mengerian

Reviewed By: #bitcoin_abc, Mengerian

Differential Revision: https://reviews.bitcoinabc.org/D14945