Update pub to use the VM's new bad-snapshot exit code.

sdk/lib/_internal/pub/test/cache/repair/updates_binstubs_test.dart

 // Copyright (c) 2014, 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 pub_tests;
 
 import 'package:scheduled_test/scheduled_test.dart';
 
 import '../../descriptor.dart' as d;
 import '../../test_pub.dart';
@@ skipping 39 matching lines @@
           Reactivating foo 1.0.0...
           Precompiling executables...
           Loading source assets...
           Precompiled foo:script.
           Installed executable foo-script.
           Reactivated 1 package.''');
 
     // The broken versions should have been replaced.
     d.dir(cachePath, [
       d.dir('bin', [
-        // 255 is the VM's exit code upon seeing an out-of-date snapshot.
-        d.matcherFile(binStubName('foo-script'), contains('255'))
+        // 253 is the VM's exit code upon seeing an out-of-date snapshot.
+        d.matcherFile(binStubName('foo-script'), contains('253'))
       ])
     ]).validate();
   });
 }