fixup! add py37 to ci

Author: mmlb

.travis.yml

@@ -4,8 +4,13 @@ python:
   - "3.4"
   - "3.5"
   - "3.6"
-  - "3.7"
 sudo: false
 
+matrix:
+  include:
+    - python: 3.7
+      dist: xenial
+      sudo: true
+
 install: pip install tox
 script: tox -e py$(echo "$TRAVIS_PYTHON_VERSION" | sed 's|\.||')