tests: errors with new pycodestyle 2.4

[stanislavlevin]

pycodestyle 2.4 was released recently and shows up new errors:

setup.py:221:2: W605 invalid escape sequence '\.'
setup.py:221:4: W605 invalid escape sequence '\.'
setup.py:221:14: W605 invalid escape sequence '\w'
setup.py:221:17: W605 invalid escape sequence '\('
setup.py:221:23: W605 invalid escape sequence '\)'
setup.py:221:25: W605 invalid escape sequence '\s'
setup.py:221:30: W605 invalid escape sequence '\s'
gssapi/raw/oids.pyx:11:13: W504 line break after binary operator
gssapi/raw/cython_converters.pxd:35:13: W504 line break after binary operator
ERROR: InvocationError for command '/bin/bash -c source ./.travis/lib-verify.sh && verify::flake8' (exited with code 1)
___________________________________ summary ____________________________________
ERROR:   py27: commands failed

Same for python3.6.