USN-5837-2: Django vulnerability

USN-5837-1 fixed a vulnerability in Django. This update provides
the corresponding update for Ubuntu 16.04 ESM.

Original advisory details:

Nick Pope discovered that Django incorrectly handled certain
Accept-Language headers. A remote attacker could possibly use this issue to
cause Django to consume memory, leading to a denial of service.

accept advisory denial of service django headers issue language memory nick pope service ubuntu update usn vulnerability