(squash with fourth commit): update error msg

convert/convert.go

@@ -93,7 +93,7 @@ func convertKongGateway2xTo3x(input *file.Content) (*file.Content, error) {
 		"From the config file, the _format_version field has been migrated from '%s' to '%s'.\n"+
 			"These automatic changes may not be fully correct or exhaustive, so please\n"+
 			"take the time to perform a manual audit of the config file.\n\n"+
-			"For related information, please visit: https://docs.konghq.com/gateway/latest/\n",
+			"For related information, please visit: https://docs.konghq.com/deck/latest/3.0-upgrade\n",
 		outputContent.FormatVersion, "3.0")
 	outputContent.FormatVersion = "3.0"
 	return outputContent, nil