I run the code

```
package main

import (
    "fmt"
    "net/http"
)

func main() {
    http.HandleFunc("/", sroot)
    http.ListenAndServe(":8080", nil)
}

func sroot(w http.ResponseWriter, r *http.Request) {
    fmt.Fprintf(w, "Welcome")
}

```

and browser showed a response as expected: `Welcome`
then, after some time I try to change the output but have found that the output does not change! so, when I change the output `fmt.Fprintf(w, "Welcome 123")` but browser still ouptuts `Welcome`.

So what's the magic happens here?