Fix --compile_all flag (--compile-all is wrong)

runtime/observatory/tests/service/vm_test.dart

 // Copyright (c) 2015, 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.
-// VMOptions=--compile-all --error_on_bad_type --error_on_bad_override
+// VMOptions=--compile_all --error_on_bad_type --error_on_bad_override
 
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
 import 'test_helper.dart';
 
 var tests = [
 
 (Isolate isolate) {
   VM vm = isolate.owner;
   expect(vm.targetCPU, isNotNull);
   expect(vm.architectureBits == 32 ||
          vm.architectureBits == 64, isTrue);
 },
 
 ];
 
 main(args) => runIsolateTests(args, tests);