Upgrade Go to 1.7.5

https://golang.org/doc/devel/release.html#go1.7.minor

go1.7.5 (released 2017/01/26) includes fixes to the compiler, runtime, and the crypto/x509 and time packages. See the Go 1.7.5 milestone on our issue tracker for details.

Patch is forthcoming, once I test it.

There is now a Go 1.8 too, but I figured you would want a 1.7.5 patch first.