fix getting css_class from self

[PetrDlouhy]

this is needed, if smart selects should work with django-crispy-forms

[coveralls]

Coverage increased (+0.02%) to 88.72% when pulling 1fb0639 on PetrDlouhy:fix_css_class into ae906b9 on digi604:master.

[blag]

Can you explain a bit more how this fixes things?

[PetrDlouhy]

The django-crispy-forms sets css class as widget.attribute:
https://github.com/django-crispy-forms/django-crispy-forms/blob/a4afab25159f229ebc667834609d5ab52d31a491/crispy_forms/templatetags/crispy_forms_field.py#L142
If smart select should work as bootstrap styled input, it needs to get class value of the self.attrs attribute.

[blag]

Merged. Thank you for the explanation and the PR!

I'll also cut a new release to PyPI shortly.