bindings: close after reading module struct

Do not let the module struct to be deallocated by `uv_dlclose`
before reading data from it.

PR-URL: https://github.com/nodejs/node/pull/2792


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Brian White <mscdex@mscdex.net>
Reviewed-By: Yosuke Furukawa <yosuke.furukawa@gmail.com>