[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