Fix #1324162 [Authors gives   error: unhandled exception  /  IndexError:string index out of range](https://bugs.launchpad.net/calibre/+bug/1324162)
version 1.39.0
Update to support Kobo firmware 3.4.1

Kobo are about to release firmware 3.4.1. The beta and release
candidates have been tested with calibre and the version number is all
that needs to change. As usual, I am bumping it to 3.4.2 in case of a
second bug fix release with no backend changes. Fixes #1324375 [Update to support Kobo firmware 3.4.1](https://bugs.launchpad.net/calibre/+bug/1324375)
pep8
Fix #1324433 [calibre, version 1.39.0 FEHLER: Problem beim Starten des wireless Gerätes: Der Wireless Treiber hat Probleme beim Starten. Problem: "start smartdevice unknown exception"](https://bugs.launchpad.net/calibre/+bug/1324433)