Install libxrender1 to appease matplotlib

Bite the bullet and preinstall it so that plotting libs that default
to using desktop rendering just work (matplotlib, ggplot, ...)
out of the box without having to get configuration right beforehand
(e.g., %matplotlib inline ahead of matplotlib import)

Only adds ~100k to the image size

(c) Copyright IBM Corp. 2015

r-notebook/Dockerfile

@@ -8,7 +8,6 @@ USER root
 # R pre-requisites
 RUN apt-get update && \
     apt-get install -y --no-install-recommends \
-    libxrender1 \
     fonts-dejavu \
     gfortran \
     gcc && apt-get clean