[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