Update pub usage of '127.0.0.1'.

sdk/lib/_internal/pub/test/test_pub.dart

Index: sdk/lib/_internal/pub/test/test_pub.dart
diff --git a/sdk/lib/_internal/pub/test/test_pub.dart b/sdk/lib/_internal/pub/test/test_pub.dart
index dbc326c3608ac083f30b13f8ce8dc038aea0f7fa..a175c7b89ac24d74956624fc9e9cc8f4ead04a4f 100644
--- a/sdk/lib/_internal/pub/test/test_pub.dart
+++ b/sdk/lib/_internal/pub/test/test_pub.dart
@@ -96,7 +96,7 @@ void serve([List<d.Descriptor> contents]) {
 
   schedule(() {
     return _closeServer().then((_) {
-      return SafeHttpServer.bind("127.0.0.1", 0).then((server) {
+      return SafeHttpServer.bind("localhost", 0).then((server) {
         _server = server;
         server.listen((request) {
           var response = request.response;