twistedchecker fails on Python 3.6

[rodrigc]

twistedchecker cannot run on Python 3.6
This must remain on Python 3.5.
If you look at the logs: https://travis-ci.org/twisted/twisted/jobs/261731629 , this error is there:

AttributeError: 'TreeRebuilder3k' object has no attribute 'visit_joinedstr'

This is fixed upstream in newer versions of pylint and astroid: pylint-dev/pylint#1113

However, twistedchecker cannot use these new versions, because it monkey patches some internals
of astroid. So we need to keep the twistedchecker stuff on Python 3.5 for now,
until we can update twistedchecker to work with newer versions of astroid.

[rodrigc]

The modifiedBlankLines() function in twistedchecker https://github.com/twisted/twistedchecker/blob/master/twistedchecker/checkers/pycodestyleformat.py#L218
monkeypatches the blank_lines() function in pycodestyle: https://github.com/PyCQA/pycodestyle/blob/master/pycodestyle.py#L302

The problem is, the newer version of pycodesyle uses a function which takes 9 arguments,
but twistedchecker's function takes 7 arguments.

So this patch no longer works.