Workaround for Python 3.7 on Travis no longer needed

Author: takluyver

.travis.yml

@@ -2,18 +2,11 @@ language: python
 
 python:
   - "nightly"
+  - "3.7"
   - "3.6"
   - "3.5"
   - "2.7"
 
-# Python 3.7 currently (early 2019) needs a newer Ubuntu version than the
-# default image on Travis.
-matrix:
-  include:
-    - python: 3.7
-      dist: xenial
-      sudo: true
-
 install:
   # We do this conditionally because it saves us some downloading if the
   # version is the same.