test: fix napi test_reference for recent V8

PR-URL: https://github.com/nodejs/node/pull/12864
Ref: https://github.com/nodejs/node/pull/12551#issuecomment-297949361


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>