Update django-anymail to 5.0

[pyup-bot]

This PR updates django-anymail[mailgun] from 4.3 to 5.0.

Changelog

5.0

----

*2018-11-07*

Breaking changes
~~~~~~~~~~~~~~~~

* **Mailgun:** Anymail's status tracking webhooks now report Mailgun "temporary failure"
events as Anymail's normalized "deferred" `event_type`. (Previously they were reported
as "bounced", lumping them in with permanent failures.) The new behavior is consistent
with how Anymail handles other ESP's tracking notifications. In the unlikely case your
code depended on "temporary failure" showing up as "bounced" you will need to update it.
(Thanks `costela`_.)

Features
~~~~~~~~

* **Postmark:** Allow either template alias (string) or numeric template id for
Anymail's `template_id` when sending with Postmark templates.

Fixes
~~~~~

* **Mailgun:** Improve error reporting when an inbound route is accidentally pointed
at Anymail's tracking webhook url or vice versa.

Links

• PyPI: https://pypi.org/project/django-anymail
• Changelog: https://pyup.io/changelogs/django-anymail/
• Repo: https://github.com/anymail/django-anymail

[coveralls]

Pull Request Test Coverage Report for Build 370

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 71.504%

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Totals
Change from base Build 367:	0.0%
Covered Lines:	1488
Relevant Lines:	2081

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💛 - Coveralls

[pyup-bot]

Closing this in favor of #160