chaperone base image is stretch

Dockerfile

@@ -21,7 +21,7 @@ COPY --from=build /go/bin/shapeshifter-dispatcher /usr/local/bin/shapeshifter-di
 COPY --from=build /usr/sbin/openvpn /usr/sbin/openvpn
 COPY --from=build /go/bin/openvpn_exporter /usr/local/bin/openvpn_exporter
 COPY chaperone.d/ /etc/chaperone.d
-RUN echo "deb http://download.opensuse.org/repositories/home:/CZ-NIC:/knot-resolver-latest/Debian_10/ /" > /etc/apt/sources.list.d/knot.list
+RUN echo "deb http://download.opensuse.org/repositories/home:/CZ-NIC:/knot-resolver-latest/Debian_9.0/ /" > /etc/apt/sources.list.d/knot.list
 COPY cznic-obs.gpg /etc/apt/trusted.gpg.d
 RUN apt-get -q update && env DEBIAN_FRONTEND=noninteractive apt-get install -y --no-install-recommends \
         openvpn libcap2-bin netcat-openbsd iptables knot-resolver knot-resolver-module-http \