sa-update is useless

Just for your information. sa-update has no influence on spamd. You must tell sa-update to reload.
```
sa-update --no-gpg --channel updates.spamassassin.org --channel spamassassin.heinlein-support.de \
    && /etc/init.d/spamassassin reload || echo "Update finish with exitcode $?"
```
my simple solution.

BTW: Have you ever proof if the bayes-db is persist outside the container? 