Get yarn to output emoji/icons on non-Mac platforms

By default, the cute magnifying glass, truck, link, etc., emoticons shown as a part of yarn‘s output in most samples only appears on OS X.

In recent versions of yarn, this can be forced on non-Mac by running:

yarn config set -- --emoji true

In most non-Mac terminals, the emojis display in monochrome.

Conversely, these icons can be disabled (on any platform) with yarn config set -- --emoji false.