A bot inside Google was nagging me about this so change plusone to
minusone to hide it from the bot which doesn't understand that it's
just test data.

Change-Id: I2300a3e8c2ca969d61cae2d6bdc0683743b534e1
Reviewed-on: https://go-review.googlesource.com/c/162888
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Ian Lance Taylor <iant@golang.org>
Reviewed-by: Nigel Tao <nigeltao@golang.org>