Try just one include directive for macOS.
language: python
+python:
+ - 2.7
+ - 3.3
+ - 3.4
+ - 3.5
matrix:
include:
- - os: linux
- python: 2.7
- - os: linux
- python: 3.3
- - os: linux
- python: 3.4
- - os: linux
- python: 3.5
- os: osx
language: generic
