Only run tests on the VM.

Now that we're using package_resolver, we aren't JS-compatible.

R=jmesserly@google.com

Review URL: https://codereview.chromium.org//2200933002 .

.test_config

diff --git a/.test_config b/.test_config
index 412fc5c..531426a 100644
--- a/.test_config
+++ b/.test_config
@@ -1,3 +1,5 @@
 {
-  "test_package": true
+  "test_package": {
+    "platforms": ["vm"]
+  }
 }
\ No newline at end of file