strings: add ReplaceAll example

Change-Id: I6b0d470bdedb92844943c8e5823e214d6a7471cf
GitHub-Last-Rev: 4a135000ba9c23a588b960e5b2989710cc71e3e2
GitHub-Pull-Request: golang/go#29199
Reviewed-on: https://go-review.googlesource.com/c/153840Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/strings/example_test.go

@@ -205,6 +205,12 @@ func ExampleReplace() {
 	// moo moo moo
 }
 
+func ExampleReplaceAll() {
+	fmt.Println(strings.ReplaceAll("oink oink oink", "oink", "moo"))
+	// Output:
+	// moo moo moo
+}
+
 func ExampleSplit() {
 	fmt.Printf("%q\n", strings.Split("a,b,c", ","))
 	fmt.Printf("%q\n", strings.Split("a man a plan a canal panama", "a "))