Add some update and clean-up steps for apt

Dockerfile

@@ -11,21 +11,23 @@ ENV PATH ${NB_PYTHON_PREFIX}/bin:$PATH
 
 # Needed for apt-key to work
 RUN apt-get update -qq --yes > /dev/null && \
- apt-get install --yes -qq gnupg2 > /dev/null
+ apt-get install --yes -qq gnupg2 > /dev/null && \
+ rm -rf /var/lib/apt/lists/*
 
 # Install TurboVNC (https://github.com/TurboVNC/turbovnc)
 ARG TURBOVNC_VERSION=2.2.6
 RUN wget -q "https://sourceforge.net/projects/turbovnc/files/${TURBOVNC_VERSION}/turbovnc_${TURBOVNC_VERSION}_amd64.deb/download" -O turbovnc.deb \
+ && apt-get update -qq --yes > /dev/null \
  && apt-get install -y ./turbovnc.deb > /dev/null \
-  # remove light-locker to prevent screen lock
+ # remove light-locker to prevent screen lock
  && apt-get remove -y light-locker > /dev/null \
  && rm ./turbovnc.deb \
- && ln -s /opt/TurboVNC/bin/* /usr/local/bin/
+ && ln -s /opt/TurboVNC/bin/* /usr/local/bin/ \
+ && rm -rf /var/lib/apt/lists/*
 
 USER ${NB_USER}
 
 COPY environment.yml /tmp/
 RUN mamba env update --name ${CONDA_ENV} -f environment.yml
 # Remove nb_conda_kernels from the env for now
 RUN mamba remove -n ${CONDA_ENV} nb_conda_kernels
-