modified dockerfile to handle file ownership

Dockerfile

@@ -23,6 +23,12 @@ RUN pip install --no-cache-dir --upgrade pip && \
 COPY notebooks/ notebooks/
 COPY data/ data/
 
+# Make sure 'jovyan' user owns these files/folders
+RUN chown -R jovyan:jovyan /home/jovyan/work
+
+# Switch back to 'jovyan' user (the default in the jupyter/docker-stacks images)
+USER $NB_UID
+
 # Expose Jupyter's default port
 EXPOSE 8888