chore: update Python versions in .travis.yml
diff --git a/.travis.yml b/.travis.yml
index 80d630e..6792d62 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -9,7 +9,9 @@
   - 3.3
   - 3.4
   - 3.5
+  - 3.6
   - pypy
+  - pypy3
 
 script:
   - python setup.py install