update postfix queue example

It looks like postfix on my machines are generating 10 character queue ids rather than the 11 in the grok example.  It appears both are legal [according to Wietse](http://tech.groups.yahoo.com/group/postfix-users/message/272316).  I get the impression from his comment less than 10 shouldn't happen, but more than 12 would be possible on disks with a very large number of inodes.