version: add go1.8rc3
version: add go1.8rc3

Change-Id: I13a9efc492905b5db0636682306e27efebb2a1bb
Reviewed-on: https://go-review.googlesource.com/35840
Reviewed-by: Brad Fitzpatrick <ae9783c0b0efc69cd85ab025ddd17aa44cdc4aa5@golang.org>

golang/build,golang/build,golang/build,golang/build