[website] update copyright year to 2022

Summary: Similar to D8887

Test Plan:
Look at calendar, see that it's now 2022
Built locally, looked at footer, says 2022 in copyright notice.

Reviewers: #bitcoin_abc, bytesofman

Reviewed By: #bitcoin_abc, bytesofman

Differential Revision: https://reviews.bitcoinabc.org/D10818