Fix broken link in swin_unetr_btcv_segmentation_3d (Project-MONAI#1674)

Fixes Project-MONAI#1672


### Checks
<!--- Put an `x` in all the boxes that apply, and remove the not
applicable items -->
- [ ] Avoid including large-size files in the PR.
- [ ] Clean up long text outputs from code cells in the notebook.
- [ ] For security purposes, please check the contents and remove any
sensitive info such as user names and private key.
- [ ] Ensure (1) hyperlinks and markdown anchors are working (2) use
relative paths for tutorial repo files (3) put figure and graphs in the
`./figure` folder
- [ ] Notebook runs automatically `./runner.sh -t <path to .ipynb file>`

Signed-off-by: YunLiu <55491388+KumoLiu@users.noreply.github.com>

3d_segmentation/swin_unetr_btcv_segmentation_3d.ipynb

@@ -100,7 +100,7 @@
     "\n",
     "![image](https://lh3.googleusercontent.com/pw/AM-JKLVLgduGZ9naCSasWg09U665NBdd3UD4eLTy15wJiwbmKLS_p5WSZ2MBcRePEJO2tv9X3TkC52MsbnomuPy5JT3vSVeCji1MOEuAzcsxily88TdbHuAt6PzccefwKupbXyOCumK5hzz5Ul38kZnlEQ84=w397-h410-no?authuser=2)\n",
     "\n",
-    "Please download the pre-trained weights from this [link](../figures/swin.png) and place it in the root directory of this tutorial. \n",
+    "Please download the pre-trained weights from this [link](https://github.com/Project-MONAI/MONAI-extra-test-data/releases/download/0.8.1/model_swinvit.pt) and place it in the root directory of this tutorial. \n",
     "\n",
     "If training from scratch is desired, please skip the step for initializing from pre-trained weights. "
    ]