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

runtime/observatory/tests/service/weak_properties_test.dart

Index: runtime/observatory/tests/service/weak_properties_test.dart
diff --git a/runtime/observatory/tests/service/weak_properties_test.dart b/runtime/observatory/tests/service/weak_properties_test.dart
index 30ae2a033535d96cfc160073c2d7d1ed2a649cf9..7de95c18f49da49f5666be547248aecd96f1b7dc 100644
--- a/runtime/observatory/tests/service/weak_properties_test.dart
+++ b/runtime/observatory/tests/service/weak_properties_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 vm_references_test;