Bump Django 2.2.11

Annonce faite sur la mailing list django-announce:

Django versions 3.0.4, 2.2.11 and 1.11.29 will be released on Wednesday, March 4, 2020 around 1000 UTC.They will fix a security defect with severity “high”.

Merge requests: !675 (merged).

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Imported from Trello