Reduce minimalistic bundles size

I've made a custom build with the following code:

```javascript
require ( 'core-js-builder' )({
  modules: ['es6.array.fill']
})
```

And the resulting build is 5.5kb, that seems **excessively** large to me. 

Isn't there a way to make it smaller? 

I would be surprised if a minified polyfill for this required more than 0.2kb, core-js' file is about 30 times larger than that.