Added def for nc 20

fpm/18/Dockerfile

@@ -17,8 +17,8 @@ RUN set -ex; \
 
 RUN set -ex; \
   savedAptMark="$(apt-mark showmanual)"; \
-  apt-get update; \
-  apt-get install -y libsmbclient-dev; \
+  apt-get --allow-unauthenticated update; \
+  apt-get --allow-unauthenticated install -y libsmbclient-dev; \
   pecl install smbclient; \
   docker-php-ext-enable smbclient; \
  # reset apt-mark's "manual" list so that "purge --auto-remove" will remove all build dependencies