Updated travis build.

Author: davidlday

.travis.yml

@@ -1,7 +1,9 @@
+dist: xenial
 language: python
 python:
-- pypy3
-- pypy
+- 'pypy3.5'
+- 'pypy'
+- '3.7'
 - '3.6'
 - '3.5'
 - '3.4'
@@ -20,5 +22,5 @@ deploy:
     secure: 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
   distributions: sdist bdist_wheel
   on:
-    python: '3.6'
+    python: '3.7'
     tags: true