non-enumerable object properties are lost after passing an object to workerize.

Here's a real life example:

``` js
// The main thread
import Worker from 'workerize-loader!./workers';
import getCompaniesFromFirebase from './getCompaniesFromFirebase';

const worker = Worker();

const {
filterCompaniesByTypes
// Other modules
} = worker;

(async () => {
const companies = await getCompaniesFromFirebase();
// typeof companies[0].id === "string" // true

const companiesFiltered = await filterCompaniesByTypes(companies, ['company-type-1', 'company-type-2']);
// typeof companiesFiltered[0].id === "string" // false
// typeof companiesFiltered[0].id === "undefined" // true
})();
```

``` js
// The worker
import intersection from 'lodash/intersection';

export const filterCompaniesByTypes = (companies, typesToFilerBy) => {
return companies.filter(({ types, id }) => {
// typeof id === 'undefined' // true
return intersection(types, typesToFilerBy).length > 0;
});
};
```

In the given example the `getCompaniesFromFirebase()` function returns an array of objects. Each object has some properties, inluding the `id` property that is non-enumerable.

After executing the `filterCompaniesByTypes()` function (which is a web worker function) I receive a filtered array. All `id` properties are gone.

---
if it's the desired behaviour (or an unpleasant, but expected, side-effect) not a bug, then it would be good to mention it in the readme.