fix Dockerfile for Binder

Dockerfile

@@ -1,16 +1,24 @@
+ARG NB_USER=jovyan
+ARG NB_UID=1000
 FROM makarius/isabelle:Isabelle2021-1
-ENV HOME=/home/isabelle/
+ENV USER ${NB_USER}
+ENV NB_UID ${NB_UID}
+ENV HOME /home/${NB_USER}
 ENV PATH=${HOME}/.local/bin/:${HOME}/Isabelle/bin/:${PATH}
 USER root
+RUN adduser --disabled-password \
+    --gecos "Default user" \
+    --uid ${NB_UID} \
+    ${NB_USER}
 RUN apt-get update
 RUN apt-get install -y python3-pip
 COPY examples/ ${HOME}/isabelle-client-examples/
 RUN chown -R isabelle ${HOME}/isabelle-client-examples/
-USER isabelle
-RUN pip install -U pip jupyterlab
+RUN python3 -m pip install --no-cache-dir notebook jupyterlab
 COPY isabelle_client/ ${HOME}/isabelle_client/
 COPY pyproject.toml ${HOME}
 COPY poetry.lock ${HOME}
 COPY README.rst ${HOME}
+USER ${NB_USER}
 RUN pip install .
 ENTRYPOINT []