Update links to cdn.net (#517)

Author: sanskar107

requirements-torch-cuda.txt

@@ -1,7 +1,7 @@
-https://s3.us-west-1.wasabisys.com/open3d-downloads/torch-1.8.2-cp36-cp36m-linux_x86_64.whl ; python_version == '3.6'
-https://s3.us-west-1.wasabisys.com/open3d-downloads/torch-1.8.2-cp37-cp37m-linux_x86_64.whl ; python_version == '3.7'
-https://s3.us-west-1.wasabisys.com/open3d-downloads/torch-1.8.2-cp38-cp38-linux_x86_64.whl ; python_version == '3.8'
-https://s3.us-west-1.wasabisys.com/open3d-downloads/torch-1.8.2-cp39-cp39-linux_x86_64.whl ; python_version == '3.9'
+https://open3d-downloads.b-cdn.net/torch-1.8.2-cp36-cp36m-linux_x86_64.whl ; python_version == '3.6'
+https://open3d-downloads.b-cdn.net/torch-1.8.2-cp37-cp37m-linux_x86_64.whl ; python_version == '3.7'
+https://open3d-downloads.b-cdn.net/torch-1.8.2-cp38-cp38-linux_x86_64.whl ; python_version == '3.8'
+https://open3d-downloads.b-cdn.net/torch-1.8.2-cp39-cp39-linux_x86_64.whl ; python_version == '3.9'
 -f https://download.pytorch.org/whl/lts/1.8/torch_lts.html
 torchvision==0.9.2+cu111
 tensorboard