JSON module is part of the core (from 5.2)

Change-Id: I0da87426145529fb7e21f2dcd3cf4a38b9432aac
Reviewed-on: http://review.couchbase.org/25660
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Reviewed-by: Mordechai Nunberg <mnunberg@haskalah.org>
Tested-by: Trond Norbye <trond.norbye@gmail.com>