The game fails to load under Firefox 77.0 with the very helpful error
message,
SyntaxError: invalid regexp group format-c2m.js:1:1
Turns out that it doesn't like the `(?<=^|\n)` lookbehind group in
the CLUE regexp. It seems lookbehind support wasn't added until FF 78,
according to the big table[1]. Switch it to a multiline regexp instead.
[1]: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions#Browser_compatibility
