[ecash-herald] Correct upgraded mock chronik client in script

Summary: Missed this as the scripts are not directly tested. Builds are failing as typescript lint catches issues here.

Test Plan: CI build, npm run build, npm test, ts-node scripts/generateMocks

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Differential Revision: https://reviews.bitcoinabc.org/D17351