Use flake8 instead of pyflakes

for additional pep8-checks

.travis.yml

@@ -8,10 +8,10 @@ matrix:
   include:
     - python: 2.7
       install:
-        - pip install pyflakes
+        - pip install flake8
         - pip install isort
       script:
-        - pyflakes tsstats/**/*.py
+        - flake8 tsstats/**/*.py
         - isort -c tsstats/**/*.py
 
 install: