regexp: add ReplaceAllStringFunc example

Change-Id: I016312f3ecf3dfcbf0eaf24e31b6842d80abb029
GitHub-Last-Rev: 360047c9006dba643429c006f89d813d927999b3
GitHub-Pull-Request: golang/go#30445
Reviewed-on: https://go-review.googlesource.com/c/164257
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>

src/regexp/example_test.go

@@ -7,6 +7,7 @@ package regexp_test
 import (
 	"fmt"
 	"regexp"
+	"strings"
 )
 
 func Example() {
@@ -204,6 +205,13 @@ func ExampleRegexp_ReplaceAllString() {
 	// -W-xxW-
 }
 
+func ExampleRegexp_ReplaceAllStringFunc() {
+	re := regexp.MustCompile(`[^aeiou]`)
+	fmt.Println(re.ReplaceAllStringFunc("seafood fool", strings.ToUpper))
+	// Output:
+	// SeaFooD FooL
+}
+
 func ExampleRegexp_SubexpNames() {
 	re := regexp.MustCompile(`(?P<first>[a-zA-Z]+) (?P<last>[a-zA-Z]+)`)
 	fmt.Println(re.MatchString("Alan Turing"))