[ecashaddrjs] Fix change log section of README

Summary:
1.5.5. was accidentally skipped in D15400

Correct this. Also match chronik-client style of change log by bulleting each version.

Test Plan: proofread

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D16337