Add pypy3 to tox.ini and .travis.yml

.travis.yml

@@ -24,6 +24,8 @@ matrix:
           env: TOXENV=py35
         - python: pypy
           env: TOXENV=pypy
+        - python: pypy3
+          env: TOXENV=pypy3
 
 install:
     - travis_retry pip install tox

tox.ini

@@ -1,6 +1,6 @@
 [tox]
 envlist =
-    cover,cover3,docs,py26,py27,py32,py33,py34,py35,pypy
+    cover,cover3,docs,py26,py27,py32,py33,py34,py35,pypy,pypy3
 
 [testenv]
 deps =