Remove Python 2.6 from Travis
language: python
matrix:
include:
- - python: "2.6"
- install: true # flake8 no longer supports Python 2.6
- before_script: flake8 () { echo flake8 disabled on Python 2.6 ; }
- python: "2.7"
- python: "3.4"
- python: "3.5"
