Fix device issue in MOO tutorial (#621)

Summary:
Fixes #615

Pull Request resolved: #621

Reviewed By: qingfeng10

Differential Revision: D25387365

Pulled By: Balandat

fbshipit-source-id: 81c75eff567678862116a75be96bc1a15ab54ca5

Author: Balandat

tutorials/multi_objective_bo.ipynb

@@ -198,7 +198,7 @@
         "        acq_func = qExpectedImprovement(  # pyre-ignore: [28]\n",
         "            model=model,\n",
         "            objective=objective,\n",
-        "            best_f=objective(train_obj).max().item(),\n",
+        "            best_f=objective(train_obj).max(),\n",
         "            sampler=sampler,\n",
         "        )\n",
         "        acq_func_list.append(acq_func)\n",