strings: Rename example to match function name.

R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/5729065
diff --git a/src/pkg/strings/example_test.go b/src/pkg/strings/example_test.go
index daeb85e..1141710 100644
--- a/src/pkg/strings/example_test.go
+++ b/src/pkg/strings/example_test.go
@@ -60,7 +60,7 @@
 	// -1
 }
 
-func ExampleRune() {
+func ExampleIndexRune() {
 	fmt.Println(strings.IndexRune("chicken", 'k'))
 	fmt.Println(strings.IndexRune("chicken", 'd'))
 	// Output: