Add missing space between words (#589)

Otherwise it's harder to copy-paste the path to the configuration.

Co-authored-by: Marcin Romaszewicz <47459980+deepmap-marcinr@users.noreply.github.com>

cmd/oapi-codegen/oapi-codegen.go

@@ -258,7 +258,7 @@ func updateConfigFromFlags(cfg configuration) (configuration, error) {
 
 	if len(unsupportedFlags) > 0 {
 		return configuration{}, fmt.Errorf("flags %s aren't supported in "+
-			"new config style, please use -old-config-style or update your configuration",
+			"new config style, please use  -old-config-style or update your configuration ",
 			strings.Join(unsupportedFlags, ", "))
 	}