Electron/React to PDF not Saving as PDF

**Describe the bug**
With Electron/React using PDFDownloadLink the Save As prompt wont allow to save as a PDF. You have to manually type .pdf

**To Reproduce**
Steps to reproduce the behavior including code snippet (if applies):

import React from 'react';
import { Page, Text, View, Document, StyleSheet, PDFDownloadLink, pdf } from '@react-pdf/renderer';

`// Create styles
const styles = StyleSheet.create({
page: {
flexDirection: 'row',
backgroundColor: '#E4E4E4',
color: '#000000'
},
section: {
margin: 0,
padding: 0,
flexGrow: 1
}
});

// Create Document Component
const PrintHeader = () => (



Section #1


Section #2



);
const PrintHeader2 = () => (

export default PrintHeader2;`

When you click on the Download now! it will prompt a save as but will not allow to save as PDF unless you manually type .PDF

**Expected behavior**
The prompt should automatically default to .PDF

**Screenshots**

**Desktop (please complete the following information):**
- OS: Windows 10
- Browser Electron / Chrome
- React-pdf version 2.13.0

Start by reproducing the issue with the provided PDFDownloadLink example in Electron/Chrome on Windows 10, using react-pdf 2.13.0. Inspect how PDFDownloadLink supplies the download filename and verify that the Save As prompt defaults to a PDF file without requiring the user to type the extension.

Written by the indexing model from the issue text.