Using togeojson with Electron (17.1.0) causes it to use the incorrect XMLserializer

This section of code (starting line 82 in togeojson.js) causes an XMLserialization error when trying to use it with Electron as the XMLSerializer shows as being defined when it needs to actually use xmldom.

```
var serializer;
if (typeof XMLSerializer !== 'undefined') {
/* istanbul ignore next */
serializer = new XMLSerializer();
// only require xmldom in a node environment
} else if (typeof exports === 'object' && typeof process === 'object' && !process.browser) {
serializer = new (require('xmldom').XMLSerializer)();
}
```

```
Uncaught TypeError: Failed to execute 'serializeToString' on 'XMLSerializer': parameter 1 is not of type 'Node'.
```

Start at togeojson.js around line 82 and inspect how the XMLSerializer is selected when running under Electron. Reproduce the serializeToString error described in the issue, then verify that Electron uses the compatible serializer and no longer reports the Node type mismatch.

Written by the indexing model from the issue text.