runtime: go fmt runtime2.go

Change-Id: I29a6125c9ef285fc365c4e11ab158b79224ae333
Reviewed-on: https://go-review.googlesource.com/126602
Run-TryBot: Martin Möhrmann <moehrmann@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>