Loosen logrotate directives for custom deployments

Logrotate refuses to rotate logfiles if /var/log/sogo has permissive write
permissions, but sometimes that is needed, especially with setups involving
multiple SOGo installs running under different UNIX users.

Scripts/logrotate

@@ -6,4 +6,5 @@
 	delaycompress
 	notifempty
 	copytruncate
+	su sogo sogo
 }