[Cashtab] Default to ABC chronik servers
Summary: Cashtab should default to abc infra. Was on chronik.be.cash in aftermath of last reindex, as this server had hotfix first.
Test Plan: npm test
Reviewers: #bitcoin_abc, Fabien
Reviewed By: #bitcoin_abc, Fabien
Differential Revision: https://reviews.bitcoinabc.org/D15078