[e.cash] Improve upgrade version wording

Summary: The website explains that node operators need to update to the latest major, but shows the latest version which is confusing. Update the wording to make it more explicit that any 0.29.x version will work.

Test Plan: See the preview.

Reviewers: #bitcoin_abc, PiRK

Reviewed By: #bitcoin_abc, PiRK

Differential Revision: https://reviews.bitcoinabc.org/D16136