test: don't use arguments.callee

Fix a strict mode violation that made the test fail to run.  It appears
to be a regression that was introduced in commit f29762f4 ("test: enable
linting for tests") which I was the sole reviewer of, so mea culpa.

PR-URL: https://github.com/nodejs/io.js/pull/2022


Reviewed-By: Rod Vagg <rod@vagg.org>
Reviewed-By: Trevor Norris <trev.norris@gmail.com>