fix for python 3.5 issue on travis

.travis.yml

@@ -13,6 +13,10 @@ branches:
   only:
     - master
 
+# update pre-installed packages
+before_install:
+  - pip list --outdated --format=freeze | grep -v '^\-e' | cut -d = -f 1  | xargs -n1 pip install -U
+
 # install package and dependencies
 install:
   - pip install coverage nose pytest pytest-cov