Updater: .hex cache directory should drop the [version] part

[dallmair]

At the moment, the Updater caches .hex files in the following directories:

• Windows: C:\Users\[currentUser]\AppData\Local\Selfbus\Selfbus-Updater\Cache\[version]
• Linux: /home/[user-home]]/.cache/Selfbus-Updater/[version]

Consequently, when updating to a new version of the Updater one loses access to all cached .hex files, which is unnecessary since those cached files to not have any dependency onto the Updater version.

Let's drop the version number part from the directory, so we can start using the diff mode even after an update of the Updater.