Tighten the check for a commonjs environment.
Tighten the check for a commonjs environment.

Looking only for a top-level `module` that is non-null incorrectly flags e.g. the `module` function [QUnit](http://qunitjs.com) 1.x. This restricts it to checking that both `module` and `exports` exists and that `module.exports === exports`, as is the case in a commonjs environment.
hiddentao/fast-levenshtein