Fix docker builds for EOL releases

stretch_php7/Dockerfile-base

@@ -1,8 +1,12 @@
-FROM debian:stretch
+FROM debian/eol:stretch
 LABEL maintainer="jan@dittberner.info"
 VOLUME /srv
 
-RUN apt-get update \
+RUN sed -i \
+      -e '/stretch-updates/d' \
+      -e 's@deb\.@archive.@' \
+      /etc/apt/sources.list \
+    && apt-get update \
     && DEBIAN_FRONTEND=noninteractive \
     apt-get install -y --no-install-recommends \
     dumb-init \