Merge pull request #62 from hroncok/py37

Problem: Docstrings were handled differently on 3.7.0b4
diff --git a/.travis.yml b/.travis.yml
index d2857cf..505745a 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -9,12 +9,8 @@
   allow_failures:
     - env: TOXENV=docstrings
   include:
-    - python: 2.6
-      env: TOXENV=py26
     - python: 2.7
       env: TOXENV=py27
-    - python: 3.3
-      env: TOXENV=py33
     - python: 3.4
       env: TOXENV=py34
     - python: 3.5