[e.cash] Swap color cashtab logos

Summary:
All wallet logos are white on /wallets except Cashtab
Rreplacing with white versions for consistency

Test Plan: preview the site and check /wallets

Reviewers: #bitcoin_abc, bytesofman

Reviewed By: #bitcoin_abc, bytesofman

Subscribers: bytesofman

Differential Revision: https://reviews.bitcoinabc.org/D16693