Change API for updateDocument to accept _id and _rev 
Change API for updateDocument to accept _id and _rev 

`updateDocument` to accept `_rev` and `_id` instead as part of the object as well as separate arguments. This makes sense as usually the documents are held in application memory with their corresponding `_rev` and `_id` properties, therefore simplifying the API.
fraserxu/react-native-couchbase-lite,fraserxu/react-native-couchbase-lite,fraserxu/react-native-couchbase-lite