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

runtime/observatory/tests/service/contexts_test.dart

Index: runtime/observatory/tests/service/contexts_test.dart
diff --git a/runtime/observatory/tests/service/contexts_test.dart b/runtime/observatory/tests/service/contexts_test.dart
index bf593f4e7610bf81cfedd8123fe3300e746e1c84..2a34ba000d714b25623ebd1dbafcf22869c2056e 100644
--- a/runtime/observatory/tests/service/contexts_test.dart
+++ b/runtime/observatory/tests/service/contexts_test.dart
@@ -1,7 +1,7 @@
 // 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
 
 library inbound_references_test;