Bump django-mptt from 0.8.7 to 0.12.0

[dependabot-preview]

Bumps django-mptt from 0.8.7 to 0.12.0.

Release notes

Sourced from django-mptt's releases.

0.9.0

• Add support for Django 1.11 and 2.0
• Drop unsupported django versions from test matrix (1.9, 1.10)
• Add Danish and Ukrainian translations
• Rollup the last year worth of minor bug fixes

Changelog

Sourced from django-mptt's changelog.

Change log

Next version

0.12

• Fixed a few bugs and added a few features.
• Reformatted the code using isort and black.
• Other, undocumented changes. Please help out.

0.11

• Changelog missing. Please help out.

0.10

• Changelog missing. Please help out.

Older versions

See the Upgrade notes section in the docs.

Commits

• f1acf9a Bump version: 0.11.0 → 0.12.0
• d1f6959 Update the CHANGELOG
• 4090141 Merge pull request #763 from ErwinJunge/multi-step-related-count
• b2de677 Merge pull request #764 from ranwise/patch-1
• 35a8c67 fix letter
• 3df545f Add support for django __ syntax to add_related_count rel_field
• 83c4201 Newer Django versions do not output the redundant script type anymore
• eeb12e6 Drop unsupported versions of Django and Python
• dc3ae8a Add Django 3.1 to the Travis CI matrix
• 77a3134 Fix #686: Use the correct database when rebuilding
• Additional commits viewable in compare view

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