Updated package to use pycodestyle

This change was originally triggered by @gvanrossum requeesting
that pep8 (the tool) be renamed to avoid confusion with PEP-8
the document. This request is tracked at:

https://github.com/PyCQA/pycodestyle/issues/466

setup.py

@@ -50,7 +50,7 @@ setup(
     packages=["flake8", "flake8.tests"],
     install_requires=[
         "pyflakes >= 0.8.1, < 1.1",
-        "pep8 >= 1.5.7, != 1.6.0, != 1.6.1, != 1.6.2",
+        "pycodestyle >= 2.0",
         "mccabe >= 0.2.1, < 0.5",
     ],
     entry_points={