Fix typo: Dummystdout != dummystdout

[blueprismo]

Hello everyone,
I have been reading through the book and I found one typo.
In this page, the following variables are shown:

var dummyBlindAlerter = &SpyBlindAlerter{}
var dummyPlayerStore = &poker.StubPlayerStore{}
var dummyStdIn = &bytes.Buffer{}
var dummyStdOut = &bytes.Buffer{}

One paragraph below, there's a typo in the reference for dummyStdOut, where the wrong value is stated: dummyStdout (bear in mind the O is in capslock). Leaving to the obvious error:

undefined: dummyStdout (compiler)