Docker: always apt-get update before apt-get install

docker/1_base/base.docker

@@ -1,7 +1,6 @@
 FROM ubuntu:16.10
 MAINTAINER Francesco Siddi <francesco@blender.org>
 
-RUN apt-get update
-RUN apt-get install -qyy \
+RUN apt-get update && apt-get install -qyy \
     -o APT::Install-Recommends=false -o APT::Install-Suggests=false \
     openssl ca-certificates

docker/3_buildwheels/build.docker

@@ -1,7 +1,7 @@
 FROM armadillica/pillar_py:3.6
 LABEL maintainer Sybren A. Stüvel <sybren@blender.studio>
 
-RUN apt-get install -qy \
+RUN apt-get update && apt-get install -qy \
     git \
     build-essential \
     checkinstall \