[jupyterhub] move npm files out of /root

jupyterhub/base/Dockerfile

@@ -16,7 +16,9 @@ RUN curl -sL https://deb.nodesource.com/setup_10.x | bash - && \
         node-gyp \
         libssl1.0-dev \
         openjdk-11-jre-headless && \
-    apt-get clean
+    apt-get clean && \
+    npm config set cache /var/cache/npm --global && \
+    npm config set update-notifier false --global
 
 RUN python${PYTHON_VERSION} -m pip install \
         jupyterlab \