Fix 2 DeprecationWarnings about invalid escape seq

[hynek]

Currently I get greeted on each test run with this:

py36 runtests: commands[0] | coverage run --parallel -m pytest
/Users/hynek/Projects/attrs/.tox/py36/lib/python3.6/site.py:165: DeprecationWarning: 'U' mode is deprecated
  f = open(fullname, "rU")
/Users/hynek/Projects/attrs/.tox/py36/lib/python3.6/site-packages/_pytest/assertion/rewrite.py:6: DeprecationWarning: the imp module is deprecated in favour of importlib; see the module's documentation for alternative uses
  import imp
/Users/hynek/Projects/attrs/.tox/py36/lib/python3.6/site-packages/_pytest/recwarn.py:118: DeprecationWarning: invalid escape sequence \d
  """
/Users/hynek/Projects/attrs/.tox/py36/lib/python3.6/site-packages/_pytest/python_api.py:604: DeprecationWarning: invalid escape sequence \d

The imp warning is probably more complicated but the other two warnings are fixed by this PR.

I don’t think it warrants a newsfragment? I can add one tho if you wish.

[RonnyPfannschmidt]

fabulous, thanks

[RonnyPfannschmidt]

will merge after a pedantic wait for ci ^^

[coveralls]

Coverage increased (+0.03%) to 92.694% when pulling acb8f23 on hynek:master into b285078 on pytest-dev:master.

[coveralls]

Coverage increased (+0.03%) to 92.694% when pulling acb8f23 on hynek:master into b285078 on pytest-dev:master.