Update PyPy version.

cf https://docs.travis-ci.com/user/languages/python/#pypy-support

This closes #9.

modified:   .travis.yml
modified:   CHANGES.rst

.travis.yml

@@ -6,7 +6,7 @@ python:
     - "3.5"
     - "3.6"
     - "pypy"
-    - "pypy3.3-5.2-alpha1"
+    - "pypy3.5"
 install:
     - pip install -U setuptools
     - pip install zc.buildout

CHANGES.rst

@@ -4,7 +4,7 @@ Changelog
 4.0.2 (unreleased)
 ------------------
 
-- Nothing changed yet.
+- Update PyPY version.
 
 
 4.0.1 (2017-11-27)