fix pypy tests on travis

Author: ikirudennis

.travis.yml

@@ -10,7 +10,8 @@ python:
   - "3.4"
   - "3.5"
   - "3.6"
-  - "pypy"
+  - "pypy-5.8"
+  - "pypy3-5.8"
 # command to install dependencies
 install:
   - if [[ $REQUIREMENTS == true ]] ; then pip install -r requirements.txt ; fi