Fix post 3.19 v8 support related wrong typedef

Change-Id: I275fcfdf502224725337221a6caf36026dbd701a
Reviewed-on: http://review.couchbase.org/31127
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>
Reviewed-by: Matt Ingenthron <matt@couchbase.com>