use older scipy version

Author: rusty1s

.travis.yml

@@ -61,6 +61,7 @@ install:
   - source script/torch.sh
   - pip install torch-scatter==latest+${IDX} -f https://s3.eu-central-1.amazonaws.com/pytorch-geometric.com/whl/torch-1.5.0.html
   - pip install flake8 codecov
+  - pip install scipy==1.4.1
   - source script/install.sh
 script:
   - flake8 .