sync: use example.com for url in ExampleWaitGroup

Fixes #48886

Change-Id: I1093ae0ba30dab5a73d4d6bcfd083564d13877a6
Reviewed-on: https://go-review.googlesource.com/c/go/+/354830
Reviewed-by: Alberto Donizetti <alb.donizetti@gmail.com>
Reviewed-by: Meng Zhuo <mzh@golangcn.org>
Trust: Alberto Donizetti <alb.donizetti@gmail.com>
diff --git a/src/sync/example_test.go b/src/sync/example_test.go
index bdd3af6..f009a68 100644
--- a/src/sync/example_test.go
+++ b/src/sync/example_test.go
@@ -22,7 +22,7 @@
 	var urls = []string{
 		"http://www.golang.org/",
 		"http://www.google.com/",
-		"http://www.somestupidname.com/",
+		"http://www.example.com/",
 	}
 	for _, url := range urls {
 		// Increment the WaitGroup counter.