Do not update incompatible apps

Previously there was no (platform) dependency check for an app that was
installed before. So Nextcloud happily upgraded an app that now requires
a php version newer than the current one. Which means in the lucky case
you see a failing upgrade due to the language incompatibility, or in the
unlucky case you see unexpected errors later in production.

Signed-off-by: Christoph Wurst <christoph@winzerhof-wurst.at>