ensure Dockerfiles use noninteractive mode when calling APT

docker/Dockerfile.conda

@@ -2,6 +2,7 @@ FROM conda/miniconda3:latest
 
 ENV LANG C.UTF-8
 ENV LC_ALL C.UTF-8
+ENV DEBIAN_FRONTEND noninteractive
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
         # all the hard non-Python dependencies

docker/Dockerfile.debian

@@ -2,6 +2,7 @@ FROM debian:latest
 
 ENV LANG C.UTF-8
 ENV LC_ALL C.UTF-8
+ENV DEBIAN_FRONTEND noninteractive
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
         gnupg dirmngr apt-transport-https ca-certificates curl software-properties-common

docker/Dockerfile.ubuntu

@@ -2,6 +2,7 @@ FROM ubuntu:16.04
 
 ENV LANG C.UTF-8
 ENV LC_ALL C.UTF-8
+ENV DEBIAN_FRONTEND noninteractive
 
 RUN apt-get update && apt-get install -y --no-install-recommends \
         gnupg dirmngr apt-transport-https software-properties-common