Update dependency django-forms-bootstrap to v3.1.0

[renovate[bot]]

This PR contains the following updates:

Package	Change	Age	Adoption	Passing	Confidence
django-forms-bootstrap	==3.0.1 -> ==3.1.0

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Release Notes

pinax/django-forms-bootstrap (django-forms-bootstrap)

### [`v3.1.0`](https://togithub.com/pinax/django-forms-bootstrap/compare/v3.0.1...v3.1.0) [Compare Source](https://togithub.com/pinax/django-forms-bootstrap/compare/v3.0.1...v3.1.0)

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