fix: read plasmashell version more reliably

In some cases, plasmashell -v crashes, which makes readAllStandardOutput fail, although the version is printed out by the process before crashing. See https://bugs.kde.org/show_bug.cgi?id=467696 and https://bugreports.qt.io/browse/QTBUG-112258 for the details of the crash. Before the crash gets fixed, a workaround for latte-dock is to wrap plasmashell -v in script, using script -q -c plasmashell\ -v, so that even if plasmashell -v crashes, the output can be read. Not being able to read plasmashell's version makes latte-dock unusable: https://github.com/NixOS/nixpkgs/issues/212828