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

runtime/observatory/tests/service/coverage_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';
 import 'dart:async';
 
 int globalVar = 100;
 
 class MyClass {
   static void myFunction(int value) {
@@ skipping 136 matching lines @@
                     expect(coverage['coverage'].length, greaterThan(100));
                 });
           }));
       return Future.wait(tests);
   });
 },
 
 ];
 
 main(args) => runIsolateTests(args, tests, testeeConcurrent: testFunction);