[Dovecot] dsync - convert plugin missing?

I'm looking to convert my mbox mailboxes over to Maildir.

But when I try to run the dsync command: (changed with my variables) dsync -u username mirror mbox:~/mail:INBOX=/var/mail/username

found on this dovecot v2.X page here: http://wiki2.dovecot.org/Migration/MailFormat

I get an error that it can't find the "convert" plugin.

Am I doing something wrong?

Thanks.