Log Message:
py-zstandard: updated to 0.13.0

Changes 0.13.0:
* ``pytest-xdist`` ``pytest`` extension is now installed so tests can be
  run in parallel.
* CI now builds ``manylinux2010`` and ``manylinux2014`` binary wheels
  instead of a mix of ``manylinux2010`` and ``manylinux1``.
* Official support for Python 3.8 has been added.
* Bundled zstandard library upgraded from 1.4.3 to 1.4.4.
* Python code has been reformatted with black.