Added multiple Python testing (Python3 and pypy)

Author: syrusakbary

.travis.yml

@@ -2,6 +2,10 @@ language: python
 sudo: false
 python:
 - 2.7
+- 3.3
+- 3.4
+- 3.5
+- pypy
 install:
 - pip install pytest pytest-cov coveralls flake8
 - pip install git+https://github.com/dittos/graphql-py.git # Last version of graphql-py