fix: replace type property with undefined except of replacing with empty string

[arturovt]

Closes #25, #39

I'm facing the same issue in the Angular application as we're using Prettier in our project that automatically adds those commas.

This is a tiny change that doesn't introduce any breaking changes. I was trying to find some documentation for Webpack's parser helpers but wasn't able to.

@developit ping.

---

Previously, tests were failing if I added comma at the end:

[developit]

I just realized this breaks the following code:

const name = 'my-worker';

new Worker('./worker.js', {
  type: "module",
  name: name
});

[developit]

@arturovt Another option might be to replace type:"module" with type:null. (toConstantDependency('type:null')).

[arturovt]

@developit

type:null is invalid as browser throws:

The provided value 'null' is not a valid enum value of type WorkerType.

Browser doesn't throw if type value is undefined.

P.S. also checked it in Chrome/Mozilla/Safari and it works perfectly.

[developit]

Brilliant @arturovt! Thank you so much for checking in other browsers.