test: add OS X to module loading error test

Previously, this test was not supported on OS X. This change makes sure
that it is no longer skipped.

PR-URL: https://github.com/nodejs/node/pull/3901


Reviewed-By: Ben Noordhuis <info@bnoordhuis.nl>
Reviewed-By: Jeremiah Senkpiel <fishrock123@rocketmail.com>
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>