USN-4967-2: nginx vulnerability

USN-4967-1 fixed a vulnerability in nginx. This update provides the corresponding update for Ubuntu 14.04 ESM and 16.04 ESM. Original advisory details: Luis Merino, Markus Vervier, and Eric Sesterhenn discovered that nginx incorrectly handled responses to the DNS resolver. A remote attacker could use this issue to cause nginx to crash, resulting in a denial of service, or possibly execute arbitrary code.