Fix docker build issue
This PR fixes docker build issue, as it looks like
debian changed `stable/update` to `stable-security/update`.
FROM debian:stable-slim
+RUN sed -i.bak s@stable/update@stable-security/update@g /etc/apt/sources.list
RUN apt-get update && apt-get -uy upgrade
RUN apt-get -y install ca-certificates && update-ca-certificates
