Only test mirror matchers on the VM (#71)

Closes #70
diff --git a/test/mirror_matchers_test.dart b/test/mirror_matchers_test.dart
index 729768e..bbd80a1 100644
--- a/test/mirror_matchers_test.dart
+++ b/test/mirror_matchers_test.dart
@@ -2,6 +2,8 @@
 // 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.
 
+@TestOn('vm')
+
 import 'package:matcher/mirror_matchers.dart';
 import 'package:test/test.dart';