Use array form for binderhub cmd
This prevents it from launching it under 'sh', which doesn't
pass signals through properly causing long termination times.
@@ -17,5 +17,5 @@ COPY --from=0 /tmp/binderhub/dist/*.whl .
COPY helm-chart/images/binderhub/binderhub_config.py .
RUN pip install --no-cache-dir *.whl
-CMD python3 -m binderhub
+CMD ["python3", "-m", "binderhub"]
EXPOSE 8585
