Zip.js function does not work on a angular implementation of the project

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Hi guys, the zip function inside ```zip.js``` does not work in a angular implementation of this package, it returns the following error:

```
MeusMapasDetailComponent.html:497 ERROR ReferenceError: process is not defined
at push../node_modules/shp-write/src/zip.js.module.exports (zip.js:33)
at Object.push../node_modules/shp-write/src/download.js.module.exports [as download] (download.js:4)
at MeusMapasDetailComponent.push../src/app/cliente-basico/modules/meus-mapas/detail/detail.component.ts.MeusMapasDetailComponent.exportshp (detail.component.ts:908)
at Object.eval [as handleEvent] (MeusMapasDetailComponent.html:497)
at handleEvent (core.js:23107)
at callWithDebugContext (core.js:24177)
at Object.debugHandleEvent [as handleEvent] (core.js:23904)
at dispatchEvent (core.js:20556)
at core.js:21003
at HTMLButtonElement. (platform-browser.js:993)
```
### My current implementation
```typescript
import * as shp from 'shp-write';
```
```typescript
getSingleGeoJson(){
var selectedPoligon = this.allDrawnItems.getLayer(this.ultimoPoligonoSelecionado.target._leaflet_id);

var newPoli = L.polygon(selectedPoligon["_latlngs"][0],
{
color: '#1DB954',
fillColor: '#1DB954',
fillOpacity: 0.2
}
).addTo(this.singlePolygonGroupLayer);

return this.singlePolygonGroupLayer.toGeoJSON();

}
```

```typescript
exportshp() {
var options = {
folder: 'myshapes',
types: {
point: 'mypoints',
polygon: 'mypolygons',
line: 'mylines'
}
}
shp.download(this.getSingleGeoJson(), options);
}
```

### What i found out
After messing arround i found that the error is in line 33 of the zip.js file inside src, where is has:
```javascript
if (!process.browser) {
generateOptions.type = 'nodebuffer';
}
```

since theres no process being set, because the method is being called by a angular project, the download does not happens.

Start by inspecting src/zip.js at line 33 and follow how src/download.js invokes it when imported from an Angular application. Reproduce the reported ReferenceError with the shown shp.download call, then verify that the browser download completes without the process error.

Written by the indexing model from the issue text.