Upgrade Django to 2.2.9 (#379)

Bump django from 2.1.7 to 2.1.11 in /requirements (#371)

Bumps [django](https://github.com/django/django) from 2.1.7 to 2.1.11.
- [Release notes](https://github.com/django/django/releases)
- [Commits](django/django@2.1.7...2.1.11)

Signed-off-by: dependabot[bot] <support@github.com>

Don't include interval value in api error response

Sort platforms by id (#377)

Have fennec always use the esr version when calculating measure summa…

…ries (#372)

Reduce fetch_measure_data interval to once every 15 minutes

Triple soft timeout limit for running celery tasks (#367)

This should make sure slow etl operations complete.

Wrap create operations that may fail in transaction.atomic (#366)

This is expected in more recent versions of django, see: https://docs.djangoproject.com/en/1.8/topics/db/transactions/#controlling-transactions-explicitly

Make "all" the default rate calculation in the subview (#355)

This is more commonly what people want to see, it seems, so let's
make it the default.

Fixes date issue in snapshot test (#339)