Travis shouldn't be installing Bokeh for Python 2.6

Author: jpivarski

.travis.yml

@@ -18,7 +18,7 @@ addons:
 
 install:
   - pip install --upgrade pip
-  - pip install bokeh
+  - if [[ $TRAVIS_PYTHON_VERSION != 2.6 ]]; then pip install bokeh; fi
 
 script:
   python setup.py test