Fix Windows preferences path

Maybe it's just on my Windows 7 box and its different on other Windows versions, but here I got an error when trying to start Tuner 0.10.2:
```
Exception in thread "main" java.lang.ExceptionInInitializerError
        at tuner.Tuner.main(Tuner.scala)
Caused by: java.io.FileNotFoundException: C:\Users\xyz\C:\Users\xyz\AppData\Roaming\UniVie Software\Tuner\prefs.json (Die Syntax für den Dateinamen, Verzeichnisnamen oder die Datenträgerbezeichnung ist falsch)
```
This pull request fixes this for me (hopefully without breaking it for other OSes, haven't had the opportunity to check yet).