drop python 3.4 support, add python 3.6

.travis.yml

@@ -5,8 +5,8 @@ notifications:
 python:
   # We don't actually use the Travis Python, but this keeps it organized.
   - "2.7"
-  - "3.4"
   - "3.5"
+  - "3.6"
 install:
   # You may want to periodically update this, although the conda update
   # conda line below will keep everything up-to-date.  We do this