Merge pull request w3c#81 from w3c/python3.7

chore: Update CI config to use Python 3.7

Author: yoavweiss

.travis.yml

@@ -1,7 +1,7 @@
 sudo: false
 language: python
 python:
-- '2.7'
+- '3.7'
 install:
 - pip install pygments lxml setuptools --upgrade
 - git clone https://github.com/tabatkins/bikeshed.git