Run builder_test only on the VM.

Necessary for Travis; no effect in google3.

PiperOrigin-RevId: 293048256
diff --git a/test/builder_test.dart b/test/builder_test.dart
index 5eb446a..5bbce3a 100644
--- a/test/builder_test.dart
+++ b/test/builder_test.dart
@@ -12,6 +12,7 @@
 // See the License for the specific language governing permissions and
 // limitations under the License.
 
+@TestOn('vm')
 import 'package:build/build.dart';
 import 'package:build_test/build_test.dart';
 import 'package:meta/meta.dart';