Update chain parameters for 0.18.8
Main chain parameters updated to a recent block.
Testnet left unchanged, as the default assume valid block is
within 10,000 block of the chain tip.
Run bitcoin-qt and check that the block hash is in the chain.
Also check that work done is correct.
Reviewers: deadalnix, jasonbcox, #bitcoin_abc
Reviewed By: jasonbcox, #bitcoin_abc
Subscribers: teamcity, schancel
Differential Revision: https://reviews.bitcoinabc.org/D2510