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

runtime/observatory/tests/service/set_library_debuggable_rpc_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
 
 library set_library_debuggable_rpc_test;
 
 import 'package:observatory/service_io.dart';
 import 'package:unittest/unittest.dart';
 
 import 'test_helper.dart';
 
 var tests = [
   (Isolate isolate) async {
@@ skipping 38 matching lines @@
       expect(e.code, equals(ServerRpcException.kInvalidParams));
       expect(e.message,
              "setLibraryDebuggable: "
              "invalid 'libraryId' parameter: libraries/9999999");
     }
     expect(caughtException, isTrue);
   },
 ];
 
 main(args) async => runIsolateTests(args, tests);