[Cashtab] Run suggested react update to bring browserslist up to date

Summary: Running npm run build in the Cashtab repo throws a warning suggesting a procedure to keep browserslist up to date. Run the suggestion.

Test Plan: Review changes to package-lock.json to verify this didn't sabotage anything

Reviewers: #bitcoin_abc, emack

Reviewed By: #bitcoin_abc, emack

Subscribers: emack

Differential Revision: https://reviews.bitcoinabc.org/D14487