fix broken syntax in requirements.txt

requirements.txt

-torch=0.4.0
-numpy=1.14.3
-torchvision=0.2.1
-scipy=1.1.0
+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=3.5.1
+pytest==3.5.1