USN-5725-2: Go vulnerability

USN-5725-1 fixed a vulnerability in Go. This update provides
the corresponding update for Ubuntu 16.04 LTS.

Original advisory details:

Diederik Loerakker, Jonny Rhea, Raúl Kripalani, and Preston
Van Loon discovered that Go incorrectly handled certain inputs.
An attacker could possibly use this issue to cause Go applications
to hang or crash, resulting in a denial of service.