don't fire ErrServerClosed on manually interrupt signals (CTRL/CMD+C)

Former-commit-id: 673c84dd13bb99c0926aa1b4a6b4eff9745403d8

_examples/http_responsewriter/write-rest/main.go

@@ -113,5 +113,5 @@ func main() {
 	//
 	// `iris.WithoutServerError` is an optional configurator,
 	// if passed to the `Run` then it will not print its passed error as an actual server error.
-	app.Listen(":8080", iris.WithoutServerError(iris.ErrServerClosed), iris.WithOptimizations)
+	app.Listen(":8080", iris.WithOptimizations)
 }