refactor: remove async library

[jimmywarting]

I only see one place where async is being used that it feels idiotic to include a such large lib just for that, it also adds a dependency of other...

I would suggest implementing that small pice of code yourself preferable by using Array.prototype@@iterator()

[bebraw]

Hi,

We can accept a PR for this. Either a lighter dep or what you described would work.

[insin]

Does async.forEach() run in parallel?

I usually reach for one of the versions someone has extracted if I need those, e.g. https://github.com/feross/run-parallel

[bebraw]

If I'm reading right, that could be written as a regular forEach. There's nothing async going on.

[insin]

I was assuming compilation.rebuildModule(module, function(err) { is async due to the errback.

[bebraw]

Ah, yeah. I missed that. Good point.

[bebraw]

That errback handling is a little weird, though, as it doesn't pass err further to terminate. It does just compilation.errors.push(err);.