Fix docker build
diff --git a/ubuntu-16.04/scripts/docker.sh b/ubuntu-16.04/scripts/docker.sh
index 780ee07..c19b624 100644
--- a/ubuntu-16.04/scripts/docker.sh
+++ b/ubuntu-16.04/scripts/docker.sh
@@ -1,10 +1,12 @@
# This should simulate preseed behavior
+apt-get update
apt-get -y install curl
echo "deb [arch=amd64] http://apt.tcpcloud.eu/nightly xenial main security extra tcp" >/etc/apt/sources.list
curl -s http://apt.tcpcloud.eu/public.gpg | apt-key add -
+apt-get clean
apt-get update
# Kernel makes no sense in docker, let base.sh know