fix docker build

Dockerfile

 FROM renku/renkulab:renku0.9.1-py3.7-0.5.2
 
-# Uncomment and adapt if code is to be included in the image
+# For some reason need to be root to install from symlink
 COPY src /code/src
+RUN ln -s /code/src
 
 # Uncomment and adapt if your R or python packages require extra linux (ubuntu) software
 # e.g. the following installs apt-utils and vim; each pkg on its own line, all lines
@@ -15,8 +16,10 @@ COPY src /code/src
 # USER ${NB_USER}
 
 # install the python dependencies
+USER root
 COPY requirements.txt environment.yml /tmp/
 RUN conda env update -q -f /tmp/environment.yml && \
     /opt/conda/bin/pip install -r /tmp/requirements.txt && \
     conda clean -y --all && \
     conda env export -n "root"
+USER ${NB_USER}