fix module.exports usage inside the module that is exporting it

[mstoykov]

During some library test/rewrite I found out that apparently

exports.a = "5";
exports.b = function() {
    return b.a;
}

Doesn't work in k6. instead of b() returning "5" it will return undefined. This has been like that at least since v0.22.1 and as far as I can see it is because of the way we load modules. This both works in node.js and goja's sample nodejs require implementaion.

Somewhat related to #1048.

[mstoykov]

fixed in #1099 merged with commit bd6d2d9