[jupyterhub] try to prevent npm from creating some files in /root

jupyterhub/base/Dockerfile

@@ -9,6 +9,7 @@ RUN apt-get update && \
         curl && \
     apt-get clean
 
+ENV NO_UPDATE_NOTIFIER=true
 RUN curl -sL https://deb.nodesource.com/setup_10.x | bash - && \
     apt-get update && \
     apt-get install -y \