Added workaround for logging to stdout

[dsexton]

See: https://github.com/moby/moby/issues/31243

[saikun]

This PR works for me. Thank.

[fredsig]

Introduced this change, but I also had to apply the following.

Dockerfile:

USER proxy

In squid.conf:

# Log to stdout
access_log stdio:/dev/stdout
pid_filename /tmp/squid.pid

https://github.com/fredsig/docker-squid/releases/tag/v3.5.27-2-stdout-2