Run tests for python 3.6-dev and nightly as well

.travis.yml

@@ -1,6 +1,8 @@
 language: python
 python:
   - "3.5"
+  - "3.6-dev"
+  - "nightly"
 install:
   - pip install -r requirements.txt
   - pip install tox
@@ -8,4 +10,4 @@ install:
 # command to run tests
 script:
   - tox
-after_success: coveralls
+after_success: coveralls