unux: use latest Debian Jessie base image and snapshot

This should not affect ABI compatibility in any way. But it does
keep our base image more secure. Not that it should matter since
we should be building every dependency from source.

Author: indygreg

cpython-unix/base.Dockerfile

@@ -1,5 +1,5 @@
 # Debian Jessie.
-FROM debian@sha256:734728c8e411698485ae644fc988dad06f757565e292b5b85edc084befa37bbb
+FROM debian@sha256:e180975d5c1012518e711c92ab26a4ff98218f439a97d9adbcd503b0d3ad1c8a
 MAINTAINER Gregory Szorc <[email protected]>
 
 RUN groupadd -g 1000 build && \
@@ -18,7 +18,7 @@ CMD ["/bin/bash", "--login"]
 WORKDIR '/build'
 
 RUN for s in debian_jessie debian_jessie-updates debian-security_jessie/updates; do \
-      echo "deb http://snapshot.debian.org/archive/${s%_*}/20200510T203930Z/ ${s#*_} main"; \
+      echo "deb http://snapshot.debian.org/archive/${s%_*}/20200930T144429Z/ ${s#*_} main"; \
     done > /etc/apt/sources.list && \
     ( echo 'quiet "true";'; \
       echo 'APT::Get::Assume-Yes "true";'; \