[Enhancement] Fix the build_segmentor in colab demo (open-mmlab#1551)

* [Enhancement] Delete DS_Store file

* [Enhancement] Fix the build_segmentor

Author: MeowZheng

demo/MMSegmentation_Tutorial.ipynb

@@ -561,8 +561,7 @@
     "datasets = [build_dataset(cfg.data.train)]\n",
     "\n",
     "# Build the detector\n",
-    "model = build_segmentor(\n",
-    "    cfg.model, train_cfg=cfg.get('train_cfg'), test_cfg=cfg.get('test_cfg'))\n",
+    "model = build_segmentor(cfg.model)\n",
     "# Add an attribute for visualization convenience\n",
     "model.CLASSES = datasets[0].CLASSES\n",
     "\n",