apparently travis doesn't support python 3.7 properly yet. this might make it work?

Author: radix

.travis.yml

@@ -5,8 +5,12 @@ python:
     - "2.7"
     - "3.4"
     - "3.5"
-    - "3.7"
     - "pypy"
+matrix:
+    include:
+        - python: 3.7
+          dist: xenial
+          sudo: true
 install:
     - pip install .
     - pip install -r dev-requirements.txt