lang/go: Mark 1.6.3 as NOT vulnerable to httpoxy

• Version 1.6.3 includes fix for "httpoxy" [1]

1: https://groups.google.com/forum/#!topic/golang-announce/7jZDOQ8f8tM

Security: cf0b5668-4d1b-11e6-b2ec-b499baebfeaf
Security: CVE-2016-5386