fix torch install

.travis.yml

@@ -5,7 +5,7 @@ jobs:
       python: 3.7
 install:
   - pip install numpy
-  - pip install torch torchvision -f https://download.pytorch.org/whl/cpu/torch-1.5.0%2Bcpu-cp37-cp37m-linux_x86_64.whl
+  - pip install torch==1.5.0+cpu torchvision==0.6.1+cpu -f https://download.pytorch.org/whl/torch_stable.html
   - pip install torch-scatter==latest+cpu -f https://pytorch-geometric.com/whl/torch-1.5.0.html
   - pip install torch-sparse==latest+cpu -f https://pytorch-geometric.com/whl/torch-1.5.0.html
   - pip install torch-spline-conv==latest+cpu -f https://pytorch-geometric.com/whl/torch-1.5.0.html