slices: use strings.EqualFold in ExampleCompactFunc

Change-Id: Ie7d495b2a53520ce89b16bc8a66b81a3955bf32f
Reviewed-on: https://go-review.googlesource.com/c/go/+/530635
Reviewed-by: Eli Bendersky <[email protected]>
Auto-Submit: Ian Lance Taylor <[email protected]>
LUCI-TryBot-Result: Go LUCI <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>

Author: ianlancetaylor

src/slices/example_test.go

@@ -51,9 +51,7 @@ func ExampleCompact() {
 
 func ExampleCompactFunc() {
 	names := []string{"bob", "Bob", "alice", "Vera", "VERA"}
-	names = slices.CompactFunc(names, func(a, b string) bool {
-		return strings.ToLower(a) == strings.ToLower(b)
-	})
+	names = slices.CompactFunc(names, strings.EqualFold)
 	fmt.Println(names)
 	// Output:
 	// [bob alice Vera]