another travisci update

Author: allmightyspiff

.travis.yml

@@ -1,3 +1,5 @@
+# https://docs.travis-ci.com/user/languages/python/#python-37-and-higher
+dist: xenial
 language: python
 sudo: false
 matrix:
@@ -8,7 +10,7 @@ matrix:
       env: TOX_ENV=py36
     - python: "3.7"
       env: TOX_ENV=py37
-    - python: "pypy3.6"
+    - python: "pypy3.5"
       env: TOX_ENV=pypy
     - python: "3.6"
       env: TOX_ENV=analysis