Log Message:
py-coverage: updated to 5.0.4

Version 5.0.4:
- If using the ``[run] relative_files`` setting, the XML report will use
  relative files in the ``<source>`` elements indicating the location of source
  code.
- The textual summary report could report missing lines with negative line
  numbers on PyPy3 7.1. This is now fixed.
- Windows wheels for Python 3.8 were incorrectly built, but are now fixed.
- Updated Python 3.9 support to 3.9a4.
- HTML reports couldn't be sorted if localStorage wasn't available. This is now
  fixed: sorting works even though the sorting setting isn't retained.