Change '127.0.0.1' to 'localhost' to support both IPv4 and IPv6 envs.

test/http_multipart_test.dart

Index: test/http_multipart_test.dart
diff --git a/test/http_multipart_test.dart b/test/http_multipart_test.dart
index 96d57026827f1f0df645c4632cedacd1a958a6eb..b113fbd85058dfb2a729584769af8fea30b22954 100644
--- a/test/http_multipart_test.dart
+++ b/test/http_multipart_test.dart
@@ -50,7 +50,7 @@ void postDataTest(List<int> message,
                   String boundary,
                   List<FormField> expectedFields,
                   {defaultEncoding: LATIN1}) {
-  HttpServer.bind("127.0.0.1", 0).then((server) {
+  HttpServer.bind("localhost", 0).then((server) {
     server.listen((request) {
       String boundary = request.headers.contentType.parameters['boundary'];
       request
@@ -86,7 +86,7 @@ void postDataTest(List<int> message,
           });
     });
     var client = new HttpClient();
-    client.post('127.0.0.1', server.port, '/')
+    client.post('localhost', server.port, '/')
         .then((request) {
           request.headers.set('content-type',
                               'multipart/form-data; boundary=$boundary');