Use --no-cache when installing ca-certificates in the Dockerfile

Signed-off-by: Dennis Marttinen <38858901+twelho@users.noreply.github.com>

docker/Dockerfile

@@ -1,6 +1,6 @@
 FROM frolvlad/alpine-glibc:glibc-2.28
 WORKDIR /app
-RUN apk update && apk add ca-certificates && rm -rf /var/cache/apk/*
+RUN apk add --no-cache ca-certificates
 ADD gotify-app /app/
 EXPOSE 80
 ENTRYPOINT ["./gotify-app"]