USN-7014-3: nginx vulnerability

USN-7014-1 fixed a vulnerability in in nginx. This update
provides the corresponding update for Ubuntu 14.04 LTS.

Original advisory details:

It was discovered that the nginx ngx_http_mp4 module incorrectly handled
certain malformed mp4 files. In environments where the mp4 directive is in
use, a remote attacker could possibly use this issue to cause nginx to
crash, resulting in a denial of service.