Merge pull request #302 from minrk/1804

bump base image to ubuntu 18.04

repo2docker/buildpacks/base.py

@@ -8,7 +8,10 @@ import logging
 import docker
 
 TEMPLATE = r"""
-FROM buildpack-deps:artful
+FROM buildpack-deps:bionic
+
+# avoid prompts from apt
+ENV DEBIAN_FRONTEND=noninteractive
 
 # Set up locales properly
 RUN apt-get update && \