test: fix up weakref.cc after v8 api change

test/gc/node_modules/weak/src/weakref.cc

@@ -134,9 +134,10 @@ void AddCallback(Handle<Object> proxy, Handle<Function> callback) {
 }
 
 
-void TargetCallback(Isolate* isolate, Persistent<Value> target, void* arg) {
+void TargetCallback(Isolate* isolate, Persistent<Object>* ptarget, void* arg) {
   HandleScope scope(isolate);
 
+  Persistent<Object> target = *ptarget;
   assert(target.IsNearDeath());
 
   proxy_container *cont = reinterpret_cast<proxy_container*>(arg);
@@ -152,7 +153,7 @@ void TargetCallback(Isolate* isolate, Persistent<Value> target, void* arg) {
 
     TryCatch try_catch;
 
-    cb->Call(target->ToObject(), 1, argv);
+    cb->Call(target, 1, argv);
 
     if (try_catch.HasCaught()) {
       FatalException(try_catch);