bump dist to one supporting python 3.7

fabianhoward · fabianhoward · commit ed978e81657c · 2018-11-27T16:22:12.000Z
diff --git a/.travis.yml b/.travis.yml
@@ -1,6 +1,6 @@
 language: python
 
-dist: precise
+dist: xenial
 
 python:
   - "3.6"
