migrate raw string to new syntax in pkg

pkg/intl/test/find_default_locale_standalone_test.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #library('find_default_locale_browser_test');
 
 #import('../lib/intl.dart');
 #import('../lib/intl_standalone.dart');
 #import('../../unittest/unittest.dart');
 
 main() {
   test("Find system locale standalone", () {
     // TODO (alanknight): This only verifies that we found some locale. We
     // should find a way to force the system locale before the test is run
     // and then verify that it's actually the correct value.
     Intl.systemLocale = "xx_YY";
     var callback = expectAsync1(verifyLocale);
     findSystemLocale().then(callback);
     });
 }
 
 verifyLocale(_) {
   expect(Intl.systemLocale, isNot(equals("xx_YY")));
-  var pattern = new RegExp(@"\w\w_[A-Z0-9]+");
+  var pattern = new RegExp(r"\w\w_[A-Z0-9]+");
   var match = pattern.hasMatch(Intl.systemLocale);
   expect(match, isTrue);
 }