2016/state-of-go/runtime: fix build tag comment breaking the build at tip

go vet failed on this in Go 1.10.

Change-Id: Ib9fc409bb0c9a6b7dd22723ee5e64470cb8f4aea
Reviewed-on: https://go-review.googlesource.com/80296
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>