Missed this one.

Update golang/go#17490.

Change-Id: I5ab2197f9981b712b37d3060f72209bebcadf291
Reviewed-on: https://go-review.googlesource.com/c/156346
Run-TryBot: Keith Randall <khr@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>