Move the flake8 config to setup.cfg

My editor (atom) reads the setup.cfg but doesn't parse the cmd-line args in the
tox.ini. So lets move the flake8 config to setup.cfg.

setup.cfg

@@ -4,3 +4,7 @@ requires = redis >= 2.7.0
 
 [wheel]
 universal = 1
+
+[flake8]
+max-line-length=120
+ignore=E731

tox.ini

@@ -20,4 +20,4 @@ basepython = python2.7
 deps =
     flake8
 commands =
-    flake8 rq tests --max-line-length=120 --ignore=E731
+    flake8 rq tests