apk used with no cache and cache update arg

[Zoey2936]

Summary

I've looked into some Dockerfiles and found: apk add --update --no-cache, which means you don't use the local cache, but at the same time update it, while not using it. I think you don't want a local cache and because of this you should remove the --update arg. (see the clamd Dockerfile as an example)

Motivation

Removing the --update arg will remove the apk index cache inside the docker image and will make it slightly slower

Additional context

https://github.com/mailcow/mailcow-dockerized/blob/master/data/Dockerfiles/clamd/Dockerfile