Update django-tables2 to 2.2.1

[pyup-bot]

This PR updates django-tables2 from 2.0.4 to 2.2.1.

Changelog

2.2.0

- Use `__` as accessor-separator, add `linkify` Meta option [702](https://github.com/jieter/django-tables2/pull/702)).
This will currently emit a warning but falls back to using `.` as separator. The next major version will raise a `ValueError` if used with `.` as separator.
- Add request attribute to table instance ([705](https://github.com/jieter/django-tables2/pull/705) by [rubickcz](https://github.com/rubickcz)).
- Append ellipsis for `LazyPaginator` if not on last page ([707](https://github.com/jieter/django-tables2/pull/707) by [tuky](https://github.com/tuky))

2.1.1

- Made `ManyToManyColumn` use `table.default` instead of a local value [680](https://github.com/jieter/django-tables2/pull/680) by [srtab](https://github.com/srtab)
- Removed invalid scope attribute in `<tr>` element of `bootstrap4.html`. [691](https://github.com/jieter/django-tables2/pull/691) by [vlt](https://github.com/vlt)
- Fixed an issue with incorrectly disabled pagination where `SingleTableMixin` was not used together with `ListView` [678](https://github.com/jieter/django-tables2/pull/678) by [nieuwenhuys](https://github.com/nieuwenhuys)

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 #496