add flake8 as test requirement

setup.py

@@ -166,7 +166,7 @@ def do_setup():
           install_requires=['numpy>=1.7.1', 'scipy>=0.11', 'six>=1.9.0'],
           # pygments is a dependency for Sphinx code highlight
           extras_require={
-              'test': ['nose>=1.3.0', 'nose-parameterized>=0.5.0'],
+              'test': ['nose>=1.3.0', 'nose-parameterized>=0.5.0', 'flake8<3'],
               'doc': ['Sphinx>=0.5.1', 'pygments']
           },
           package_data={