Typo removal (Project-MONAI#662)

Author: JK-rez

3d_segmentation/spleen_segmentation_3d.ipynb

@@ -409,7 +409,7 @@
     "train_ds = CacheDataset(\n",
     "    data=train_files, transform=train_transforms,\n",
     "    cache_rate=1.0, num_workers=4)\n",
-    "# train_ds = monai.data.Dataset(data=train_files, transform=train_transforms)\n",
+    "# train_ds = Dataset(data=train_files, transform=train_transforms)\n",
     "\n",
     "# use batch_size=2 to load images and use RandCropByPosNegLabeld\n",
     "# to generate 2 x 4 images for network training\n",