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

runtime/observatory/tests/service/gc_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.
-// 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 'test_helper.dart';
 
 import 'dart:async';
 
 void script() {
   var grow;
   grow = (int iterations, int size, Duration duration) {
     if (iterations <= 0) {
@@ skipping 21 matching lines @@
         completer.complete();
       }
     });
   });
   return completer.future;
 },
 
 ];
 
 main(args) => runIsolateTests(args, tests, testeeConcurrent: script);