add TOXENV=py37

.travis.yml

@@ -1,20 +1,23 @@
 sudo: false
 language: python
-python: 3.5
 cache:
   directories:
     - $HOME/.cache/pip
 
 matrix:
-    include:
-        - python: 2.7
-          env: TOXENV=py27
-        - python: 3.4
-          env: TOXENV=py34
-        - python: 3.5
-          env: TOXENV=py35
-        - python: 3.6
-          env: TOXENV=py36
+  include:
+    - python: 2.7
+      env: TOXENV=py27
+    - python: 3.4
+      env: TOXENV=py34
+    - python: 3.5
+      env: TOXENV=py35
+    - python: 3.6
+      env: TOXENV=py36
+    - env: TOXENV=py37
+      python: nightly
+  allow_failures:
+    - python: nightly
 
 install:
     - pip install -U tox nose cython

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py27, py34, py35, py36
+envlist = py27, py34, py35, py36, py37
 
 [testenv]
 commands =