fix "Release file expired"

Dockerfile

 FROM continuumio/miniconda
 MAINTAINER Bas Nijholt <bas@nijho.lt>
 
-RUN apt-get update -q && apt-get install -qy \
+RUN apt-get -o Acquire::Check-Valid-Until=false update -q && apt-get install -qy \
     texlive-full \
     python-pygments gnuplot \
     make git \