Update pytest to 3.3.2

[pyup-bot]

There's a new version of pytest available.
You are currently using 3.3.1. I have updated it to 3.3.2

These links might come in handy: PyPI | Changelog | Repo | Homepage

Changelog

3.3.2

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

Bug Fixes

• pytester: ignore files used to obtain current user metadata in the fd leak
  detector. (2784 <https://github.com/pytest-dev/pytest/issues/2784>_)

• Fix memory leak where objects returned by fixtures were never destructed
  by the garbage collector. (2981 <https://github.com/pytest-dev/pytest/issues/2981>_)

• Fix conversion of pyargs to filename to not convert symlinks and not use
  deprecated features on Python 3. (2985 <https://github.com/pytest-dev/pytest/issues/2985>_)

• PYTEST_DONT_REWRITE is now checked for plugins too rather than only for
  test modules. (2995 <https://github.com/pytest-dev/pytest/issues/2995>_)

Improved Documentation

• Add clarifying note about behavior of multiple parametrized arguments (3001 <https://github.com/pytest-dev/pytest/issues/3001>_)

Trivial/Internal Changes

• Code cleanup. (3015 <https://github.com/pytest-dev/pytest/issues/3015>,
  3021 <https://github.com/pytest-dev/pytest/issues/3021>)

• Clean up code by replacing imports and references of _ast to ast. (3018 <https://github.com/pytest-dev/pytest/issues/3018>_)

Got merge conflicts? Close this PR and delete the branch. I'll create a new PR for you.

Happy merging! 🤖