update requirements.txt to pytorch 0.4

requirements.txt

-torch
-numpy
-torchvision
-scipy
+torch=0.4.0
+numpy=1.14.3
+torchvision=0.2.1
+scipy=1.1.0
 gitpython
 git+https://github.com/pytorch/tnt.git@master
 tensorflow==1.7.0
@@ -15,4 +15,4 @@ graphviz==0.8.2
 ipywidgets==7.1.2
 bqplot==0.10.5
 pyyaml
-pytest
+pytest=3.5.1