According to the POSIX Programmer's Manual, the exit status specified by
the unsigned decimal integer. If n is specified, but its value is not
between 0 and 255 inclusively, the exit status is undefined.
By cross reference the usage between different scripts in this project,
it looks like we could simply remove the `-` before the number.
As there is `apk upgrade` and `apk update`, the apk index will already
be existed. `--no-cache` is for `apk` when there is no `apk update`
behavior and it's expected to be no local cache left, not suitable for
the use case here, which wants to upgrade all the package to the latest
when packaging the image.