Use --privileged instead of --cap-add=sys_admin due to build error

Encountring the following errors with --cap-add=sys_admin inside the dj_make_chroot script; one inside the debootstrap, and the other somewhere inside the script itself:

...
W: Failure trying to run: chroot "/chroot/domjudge" mount -t proc proc /proc
W: See /chroot/domjudge/debootstrap/debootstrap.log for details
...
mount: /chroot/domjudge/proc: cannot mount proc read-only.
       dmesg(1) may have more information after failed mount system call.
...

The /chroot/domjudge/debootstrap/debootstrap.log does not exist nor the dmesg to investigate further (naive approach OFC).

docker/build-judgehost.sh

@@ -12,7 +12,7 @@ docker build -t "${docker_tag}-build" -f judgehost/Dockerfile.build .
 # Build chroot
 builder_name=$(echo "${docker_tag}" | sed 's/[^a-zA-Z0-9_-]/-/g')
 docker rm -f "${builder_name}" > /dev/null 2>&1 || true
-docker run --name "${builder_name}" --cap-add=sys_admin "${docker_tag}-build"
+docker run --name "${builder_name}" --privileged "${docker_tag}-build"
 docker cp "${builder_name}:/chroot.tar.gz" .
 docker cp "${builder_name}:/judgehost.tar.gz" .
 docker rm -f "${builder_name}"