update runner in d2go_beginner script

Summary:
Pull Request resolved: https://github.com/facebookresearch/d2go/pull/76

Detectron2GoRunner doesn't contain configs about exporting RCNN models, use GeneralizedRCNNRunner instead

Reviewed By: zhanghang1989

Differential Revision: D28652627

fbshipit-source-id: 6f324f608d8b2abdf98179a36e4b79837f135340

demo/d2go_beginner.ipynb

@@ -421,11 +421,11 @@
     }
    ],
    "source": [
-    "from d2go.runner import Detectron2GoRunner\n",
+    "from d2go.runner import GeneralizedRCNNRunner\n",
     "\n",
     "\n",
     "def prepare_for_launch():\n",
-    "    runner = Detectron2GoRunner()\n",
+    "    runner = GeneralizedRCNNRunner()\n",
     "    cfg = runner.get_default_cfg()\n",
     "    cfg.merge_from_file(model_zoo.get_config_file(\"faster_rcnn_fbnetv3a_C4.yaml\"))\n",
     "    cfg.MODEL_EMA.ENABLED = False\n",
@@ -709,4 +709,4 @@
  },
  "nbformat": 4,
  "nbformat_minor": 4
-}
+}
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