Update pytest to 3.9.3

[pyup-bot]

This PR updates pytest from 3.9.2 to 3.9.3.

Changelog

3.9.3

=========================

Bug Fixes
---------

- `4174 <https://github.com/pytest-dev/pytest/issues/4174>`_: Fix "ValueError: Plugin already registered" with conftest plugins via symlink.


- `4181 <https://github.com/pytest-dev/pytest/issues/4181>`_: Handle race condition between creation and deletion of temporary folders.


- `4221 <https://github.com/pytest-dev/pytest/issues/4221>`_: Fix bug where the warning summary at the end of the test session was not showing the test where the warning was originated.


- `4243 <https://github.com/pytest-dev/pytest/issues/4243>`_: Fix regression when ``stacklevel`` for warnings was passed as positional argument on python2.



Improved Documentation
----------------------

- `3851 <https://github.com/pytest-dev/pytest/issues/3851>`_: Add reference to ``empty_parameter_set_mark`` ini option in documentation of ``pytest.mark.parametrize``



Trivial/Internal Changes
------------------------

- `4028 <https://github.com/pytest-dev/pytest/issues/4028>`_: Revert patching of ``sys.breakpointhook`` since it appears to do nothing.


- `4233 <https://github.com/pytest-dev/pytest/issues/4233>`_: Apply an import sorter (``reorder-python-imports``) to the codebase.


- `4248 <https://github.com/pytest-dev/pytest/issues/4248>`_: Remove use of unnecessary compat shim, six.binary_type

Links

• PyPI: https://pypi.org/project/pytest
• Changelog: https://pyup.io/changelogs/pytest/
• Homepage: https://docs.pytest.org/en/latest/