chore(tests): Also run tests on Python 2.6

.travis.yml

@@ -1,6 +1,7 @@
 ---
 language: python
 python:
+  - 2.6
   - 2.7
   - 3.3
   - 3.4
@@ -9,9 +10,10 @@ python:
   - nightly
 install:
   - pip install pyyaml flake8 flake8-import-order coveralls
+  - if [[ $TRAVIS_PYTHON_VERSION == 2.6 ]]; then pip install unittest2; fi
   - pip install .
 script:
-  - flake8 .
+  - if [[ $TRAVIS_PYTHON_VERSION != 2.6 ]]; then flake8 .; fi
   - yamllint --strict $(git ls-files '*.yaml' '*.yml')
   - coverage run --source=yamllint setup.py test
 after_success: