moretypes: remove reference to math.Pow (it's meant to be xor)

Fixes golang/go#11231

Change-Id: Id2d85520d18bc42c1c08061a2f98a88255e6adf8
Reviewed-on: https://go-review.googlesource.com/11134
Reviewed-by: Ian Lance Taylor <iant@golang.org>
1 file changed