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 like what you're suggesting: it's both easy to read and should be quite efficient. 
But do != -1 : since ```indexOf``` starts at 0, testing for >0 would actually miss types starting with Book or Dissertation.