corrected 'imap_getmailboxes' comment to include third parameter (#1663)

examples/gmail.phps

@@ -81,7 +81,7 @@ if (!$mail->send()) {
 //Section 2: IMAP
 //IMAP commands requires the PHP IMAP Extension, found at: https://php.net/manual/en/imap.setup.php
 //Function to call which uses the PHP imap_*() functions to save messages: https://php.net/manual/en/book.imap.php
-//You can use imap_getmailboxes($imapStream, '/imap/ssl') to get a list of available folders or labels, this can
+//You can use imap_getmailboxes($imapStream, '/imap/ssl', '*' ) to get a list of available folders or labels, this can
 //be useful if you are trying to get this working on a non-Gmail IMAP server.
 function save_mail($mail)
 {