[website] Make CashFusion one word

Summary:
After looking at the history, I realized CashFusion should be one word.
This makes it consistent with Electrum ABC GUI and source code, and also other places such as https://cashfusion.org/

Test Plan:
git grep "Cash Fusion"
Ran the site locally to look at it.

Reviewers: PiRK, #bitcoin_abc, bytesofman

Reviewed By: #bitcoin_abc, bytesofman

Differential Revision: https://reviews.bitcoinabc.org/D11695