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 wouldn't worry about performance between switch and if-else. The difference should be trivial, if there's one at all. I like using switch statements because they make the code less cluttered (at least I think so), but otherwise, if-else is perfectly fine.