cross.js: get clues via textContent instead of innerHTML to avoid HTML encoding and stray html tags

[maiamcc]

👋what an excellent project!

Dropping this PR here because I was getting annoyed by clues exporting as

"Law & Order" spinoff, briefly

and also it seemed that any stray HTML tags that ended up in a clue due to copy-paste being impossible to get rid of.

Couldn't test it very thoroughly because I ran into problems generating xwsolve.js and gave up, but I think this does the trick.