Update ProQuest.js

See https://forums.zotero.org/discussion/40821/zotero-not-recognizing-books-chapters-dissertations-in-proquest-psycinfo/

(Maybe we should wait for more examples of different types.)
I would maybe just split on `,` and take the first part. That would fix the `Chapter` match above, reduce these two lines to "Book", but we'd need to add "Handbook/manual". Of course, as you suggest, if we can come up with more robust logic, like using regexp to look for `/(?:^|,\s*)Chapter\s*(?:,|$)/` first, then `/(?:^|,\s*)Book\s*(?:,|$)/` before hitting the switch statement, that would be good too.

Also, I'm not sure this belongs as a "guess". Seems like "Book, Edited Book" is fairly clearly a "book".