Incorrect embedding of reference urls in SiamMask guide.

**Description**
Reference urls in [SiamMask guide](https://github.com/Esri/arcgis-python-api/blob/master/guide/14-deep-learning/track_objects_using_SiamMask.ipynb) have incorrect formatting which leads to broken links and page not found errors.

**To Reproduce**

- Download the notebook.
- Follow the reference urls.

**Expected behavior**
The urls should have valid formatting.
