Fix wrong user for apt-get in r-notebook

r-notebook/Dockerfile

@@ -3,7 +3,7 @@ FROM jupyter/minimal-notebook
 
 MAINTAINER Jupyter Project <jupyter@googlegroups.com>
 
-USER jovyan
+USER root
 
 # R pre-requisites
 RUN apt-get update && \
@@ -13,6 +13,8 @@ RUN apt-get update && \
     gfortran \
     gcc && apt-get clean
 
+USER jovyan
+
 # R packages
 RUN conda config --add channels r
 RUN conda install --yes \