optimize example code

examples/main.go

@@ -33,14 +33,14 @@ import (
 
 var sum int32
 
-func myFunc(i interface{}) error {
+func myFunc(i interface{}) {
 	n := i.(int32)
 	atomic.AddInt32(&sum, n)
 	fmt.Printf("run with %d\n", n)
 	return nil
 }
 
-func demoFunc() error {
+func demoFunc() {
 	time.Sleep(10 * time.Millisecond)
 	fmt.Println("Hello World!")
 	return nil