doc: update go1.8.html after feedback from Russ

Address Russ's feedback from https://golang.org/cl/33244

TBR=See https://golang.org/cl/33244

Updates #17929

Change-Id: I708d71f519f6414ecec629d3c273d9e737d8ed50
Reviewed-on: https://go-review.googlesource.com/33656
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

Author: bradfitz