Update django-tables2 to 1.4.1

[pyup-bot]

There's a new version of django-tables2 available.
You are currently using 1.3.0. I have updated it to 1.4.1

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

Changelog

1.4.1

• Fix urls to screenshots in on pypi description (fixes 398)
• Prevent superfluous spaces when a callable row_attrs['class'] returns an empty string ([417](Check for empty string on row_attrs['class'] jieter/django-tables2#417 by Superman8218), fixes 416)

1.4.0

• Return None from Table.as_values() for missing values. 419
• Fix ordering by custom fields, and refactor TableData 424, fixes 413
• Revert removing TableData.__iter__() (removed in this commit), fixes 427, 361 and 421.

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

Happy merging! 🤖