src: fix Persistent<> deprecation warning

Pass the Isolate to Persistent<Function>::New(). Fixes the following
warning:

  ../../src/node.cc: In function ‘v8::Handle<v8::Value>
  node::UsingDomains(const v8::Arguments&)’:
  ../../src/node.cc:921: warning: ‘New’ is deprecated
  declared at ../../deps/v8/include/v8.h:4438)

src/node.cc

@@ -918,7 +918,7 @@ Handle<Value> UsingDomains(const Arguments& args) {
   Local<Function> ndt = ndt_v.As<Function>();
   process->Set(String::New("_tickCallback"), tdc);
   process->Set(String::New("nextTick"), ndt);
-  process_tickCallback = Persistent<Function>::New(tdc);
+  process_tickCallback = Persistent<Function>::New(node_isolate, tdc);
   return Undefined();
 }