fix travis-ci python3.7 build

diff --git a/.travis.yml b/.travis.yml
index 1d7f26a370954f0183b343516d92d1e7dd9a0f6a..846a502466f6531113e9812c8ca03dfd42437361 100644 (file)
--- a/.travis.yml
+++ b/.travis.yml
@@ -3,13 +3,18 @@ sudo: false
 language: python
 
 python:
-  - "3.7"  
-  - "3.6"  
+  - "3.6"
   - "3.5"
   - "3.4"
   - "2.7"
   - "pypy"
 
+matrix:
+  include:
+    - python: 3.7
+      dist: xenial
+      sudo: true
+
 # command to install dependencies, e.g. pip install -r requirements.txt --use-mirrors
 install: pip install -r requirements.txt