Fix col offset

[kaste]

mypy changed the col base. We need to normalize this column to the base flake8 expects.

Tested with mypy-0.610

E.g. before the patch

> type plugin.py | C:\Dev\python36\Scripts\flake8.exe --format default -
C:\Users\c-flo\AppData\Local\Temp\flake8mypy_ynlp41vb\tmpmypy_06s72jce.py:17:1: error: Need type annotation for 'KNOWN_WINDOWS'
C:\Users\c-flo\AppData\Local\Temp\flake8mypy_ynlp41vb\tmpmypy_06s72jce.py:53:18: error: "str" has no attribute "window"

stdin:17:2: T484 Need type annotation for 'KNOWN_WINDOWS'
stdin:53:19: T484 "str" has no attribute "window"

First comes the raw stdout from mypy. You can see that mypy reports 17:1 but the flake8 output indicates an error at 17:2

This patch of course reduces the failing Travis CI. And, unfortunately, this is again on top of my previous PR, but you can cherry-pick whatever you want. And the commits are tiny.

[kaste]

Replaces #15