examples: replace all app.Run(iris.Addr(...)) with app.Listen just for the shake of simplicity, both are doing the same exact thing as it's described on the http listening first example.

Former-commit-id: d20afb2e899aee658a8e0ed1693357798df93462

_examples/sessions/flash-messages/main.go

@@ -38,5 +38,5 @@ func main() {
 		ctx.Writef(", and again from the same context: %s", name)
 	})
 
-	app.Run(iris.Addr(":8080"))
+	app.Listen(":8080")
 }