Create /usr/share/exim4 since it's no longer created.

exim4/Dockerfile

@@ -19,6 +19,7 @@ RUN apt-get update && \
     install -d -o Debian-exim -g Debian-exim -m 755 /var/lib/exim4/ && \
     install -o root -g ssl-cert -m 664 /dev/null /etc/ssl/certs/ssl-cert-snakeoil.pem && \
     install -o root -g ssl-cert -m 664 /dev/null /etc/ssl/private/ssl-cert-snakeoil.key && \
+    install -d -o root -g root -m 755 /usr/share/exim4 && \
     install -o root -g ssl-cert -m 664 /dev/null /usr/share/exim4/dh.pem && \
     setcap CAP_NET_BIND_SERVICE=+ep /usr/sbin/exim4 && \
     rm -rf /usr/share/exim4/dh.pem /var/lib/exim4/config.autogenerated /etc/exim4/* && \