Downgrade torch on mac to 1.8.1 (#436)

* Downgrade torch on mac to 1.8.1
* Update CI to use old CXX11_ABI due to new CXX11_ABI default in Open3D.
Co-authored-by: Sameer Sheorey <sameer.sheorey@intel.com>

Author: errissa

ci/run_ci.sh

@@ -38,6 +38,7 @@ mkdir Open3D/build
 pushd Open3D/build
 cmake -DBUNDLE_OPEN3D_ML=ON \
     -DOPEN3D_ML_ROOT=$PATH_TO_OPEN3D_ML \
+    -DGLIBCXX_USE_CXX11_ABI=OFF \
     -DBUILD_TENSORFLOW_OPS=ON \
     -DBUILD_PYTORCH_OPS=ON \
     -DBUILD_GUI=OFF \

requirements-torch.txt

@@ -1,6 +1,6 @@
 -f https://download.pytorch.org/whl/lts/1.8/torch_lts.html
 torch==1.8.2+cpu ; sys_platform != 'darwin'
 torchvision==0.9.2+cpu ; sys_platform != 'darwin'
-torch==1.8.2 ; sys_platform == 'darwin'
+torch==1.8.1 ; sys_platform == 'darwin'
 torchvision==0.9.1 ; sys_platform == 'darwin'
 tensorboard