[Cashtab] Extension version bump

Summary:
Bump extension version. To be built and submitted for review at app store.

Now that Cashtab.com is off ecashjs-lib, the extension should be as well.

Test Plan: Follow plan to build extension locally in Cashtab's README. Create a wallet and send txs.

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D13700