Docker: Fix "Failed export and unexpected container restart"

- Fixes #4089

Also this was broken too:

docker-compose exec wekandb apt-get update

because /tmp didn't exist, it was introduced by this commit:
1322c1fbbd

Dockerfile

@@ -309,7 +309,7 @@ RUN \
     apt-get remove --purge -y ${BUILD_DEPS} && \
     apt-get autoremove -y && \
     npm uninstall -g api2html &&\
-    rm -R /tmp* && \
+    rm -R /tmp/* && \
     rm -R /var/lib/apt/lists/* && \
     rm -R /home/wekan/.meteor && \
     rm -R /home/wekan/app && \