Fix bugs in indexed interceptor test.

Returning a string in the enumerator was never allowed but wasn't
enforced until recently.  In Node.js 10, it hits a CHECK in V8.

test/cpp/indexedinterceptors.cpp

@@ -96,7 +96,7 @@ NAN_INDEX_SETTER(IndexedInterceptor::PropertySetter) {
 
 NAN_INDEX_ENUMERATOR(IndexedInterceptor::PropertyEnumerator) {
   v8::Local<v8::Array> arr = Nan::New<v8::Array>();
-  Set(arr, 0, Nan::New("whee").ToLocalChecked());
+  Set(arr, 0, Nan::New(42));
   info.GetReturnValue().Set(arr);
 }
 
@@ -111,6 +111,9 @@ NAN_INDEX_QUERY(IndexedInterceptor::PropertyQuery) {
   if (index == 1) {
     info.GetReturnValue().Set(Nan::New<v8::Integer>(v8::DontEnum));
   }
+  if (index == 42) {
+    info.GetReturnValue().Set(Nan::New(0));
+  }
 }
 
 NODE_MODULE(indexedinterceptors, IndexedInterceptor::Init)

test/js/indexedinterceptors-test.js

@@ -19,5 +19,5 @@ test('indexedinterceptors', function (t) {
   delete interceptor[0];
   t.equal(interceptor[0], 'goober');
   t.ok(Object.prototype.hasOwnProperty.call(interceptor, 1));
-  t.equal(Object.keys(interceptor)[0], 'whee');
+  t.equal(Object.keys(interceptor)[0], '42');
 });