Better the flatpak-daily script.

- More scripty (set -eu, not just an alias in a script).
- Update appstream data.

Documents/bin/flatpak-daily

 #!/bin/sh
-flatpak update --assumeyes --appstream && flatpak uninstall --unused --assumeyes
+set -eu
+
+flatpak update --appstream
+flatpak update --assumeyes
+flatpak uninstall --unused --assumeyes