Update django-tables2 to 2.1.0

[pyup-bot]

This PR updates django-tables2 from 2.0.4 to 2.1.0.

Changelog

2.1.0

- Dropped support for python 2.7 (and django 1.11).
- Removed `django_tables2.utils.ucfirst`, use `django.utils.text.capfirst` instead.
- Removed `class="thead-default"` from bootstrap4 template ([671](https://github.com/jieter/django-tables2/issues/671))
- Included columns with `visible=False` in export ([677](https://github.com/jieter/django-tables2/pull/677))
- Fixed pagination when the number of pages is equal to page range plus one ([655](https://github.com/jieter/django-tables2/pull/655))

2.0.6

-  Add optional 'table' kwarg to `row_attrs` callables

2.0.5

- Fixes issue with wrong time format for TimeColumn [650](https://github.com/jieter/django-tables2/pull/650) by [IgorCode](https://github.com/IgorCode)

Links

• PyPI: https://pypi.org/project/django-tables2
• Changelog: https://pyup.io/changelogs/django-tables2/
• Repo: https://github.com/jieter/django-tables2/

[pyup-bot]

Closing this in favor of #174