Use conda torchvision version (#20865)
Summary:
This tries to fix the following error on current master:
```
May 23 16:18:47 Traceback (most recent call last):
May 23 16:18:47 File "main.py", line 7, in <module>
May 23 16:18:47 from torchvision import datasets, transforms
May 23 16:18:47 File "/opt/conda/lib/python3.6/site-packages/torchvision/__init__.py", line 1, in <module>
May 23 16:18:47 from torchvision import models
May 23 16:18:47 File "/opt/conda/lib/python3.6/site-packages/torchvision/models/__init__.py", line 11, in <module>
May 23 16:18:47 from . import detection
May 23 16:18:47 File "/opt/conda/lib/python3.6/site-packages/torchvision/models/detection/__init__.py", line 1, in <module>
May 23 16:18:47 from .faster_rcnn import *
May 23 16:18:47 File "/opt/conda/lib/python3.6/site-packages/torchvision/models/detection/faster_rcnn.py", line 7, in <module>
May 23 16:18:47 from torchvision.ops import misc as misc_nn_ops
May 23 16:18:47 File "/opt/conda/lib/python3.6/site-packages/torchvision/ops/__init__.py", line 1, in <module>
May 23 16:18:47 from .boxes import nms, box_iou
May 23 16:18:47 File "/opt/conda/lib/python3.6/site-packages/torchvision/ops/boxes.py", line 2, in <module>
May 23 16:18:47 from torchvision import _C
May 23 16:18:47 ImportError: /opt/conda/lib/python3.6/site-packages/torchvision/_C.cpython-36m-x86_64-linux-gnu.so: undefined symbol: _ZN2at19NonVariableTypeMode10is_enabledEv
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/20865
Differential Revision: D15481736
Pulled By: yf225
fbshipit-source-id: 67d4fd70652ccc709b44cb15392d6e44a8fe9235
