We still support Go 1.6 for a few more days. (it'd normally be dropped
after Go 1.9 final is out)

And maybe we'll need to make a special case for supporting it longer
than normal if gRPC needs to.

Change-Id: I78675f1ef26aa09436a70d0f8aa3a0958768dd14
Reviewed-on: https://go-review.googlesource.com/53641Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>