Update Travis config

.travis.yml

@@ -1,10 +1,12 @@
 language: python
 
 python:
+  - 2.6
   - 2.7
   - 3.3
   - 3.4
   - 3.5
+  - 3.6
   - pypy
   - pypy3
 
@@ -15,4 +17,5 @@ script: python setup.py test
 
 install:
     # Temporary solution for Travis CI multiprocessing issue #943
+    # https://github.com/travis-ci/travis-ci/issues/943
     - sudo rm -rf /dev/shm && sudo ln -s /run/shm /dev/shm