Update chainparams for 0.18.7

Summary: Skipped updating testnet chainparams since it appears to have undergone a large reorg recently.

Test Plan: Verify the updated params according to your own nodes.

Reviewers: deadalnix, Fabien, Mengerian, #bitcoin_abc

Reviewed By: Fabien, #bitcoin_abc

Subscribers: teamcity, schancel

Differential Revision: https://reviews.bitcoinabc.org/D2413