When auto-upgrading a v3 remote, avoid upgrading to version 6, instead keep it at version 5.

Fixes a bug introduced with v6 mode that I didn't notice until now.
Probably not many v3 repos left out there, and upgrading them to v6 mode
is not disastrous, only a little premature.

This commit was sponsored by Riku Voipio

Command/Upgrade.hs

@@ -26,5 +26,5 @@ start = do
 	showStart "upgrade" "."
 	whenM (isNothing <$> getVersion) $ do
 		initialize Nothing Nothing
-	r <- upgrade False
+	r <- upgrade False latestVersion
 	next $ next $ return r