Remove Ubuntu distribution specification for Travis CI

Xenial is now the default:
https://blog.travis-ci.com/2019-04-15-xenial-default-build-environment
https://changelog.travis-ci.com/xenial-as-the-default-build-environment-is-coming-97772

diff --git a/.travis.yml b/.travis.yml
index 86b7752008ae8825b117bd02bf8017ed78ac870d..9580c7145bc798bfb3d4dea48614f70594b3b572 100644 (file)
--- a/.travis.yml
+++ b/.travis.yml
@@ -5,12 +5,10 @@ python:
 - '2.7'
 - '3.5'
 - '3.6'
+- '3.7'
 
 matrix:
   fast_finish: true
-  include:
-    - python: 3.7
-      dist: xenial
 
 env:
   global: