Update pytorch

relaxed constraints on both pytorch and torchvision:

• pytorch >= 0.4.0 (instead of ==)
• torchvision >= 0.2.0 (instead of ==)

Updated the CI (dropping out Python 2)

conda/meta.yaml

@@ -30,8 +30,8 @@ requirements:
     - python
     - setuptools
     - numpy >=1.11
-    - pytorch =0.4
-    - torchvision =0.2.0
+    - pytorch >=0.4
+    - torchvision >=0.2.0
 test:
   imports:
     - {{ name }}