Update examples to use `this.request.body` from `koa-better-body`

[cat2608]

Using koa-better-body we must to add the option 'fields': 'body'due koa-validation requires this.request.body instead this.body:

app.use(koaBody({
    'multipart': true,
    'fields': 'body',
}));

https://github.com/srinivasiyer/koa-validation/blob/master/lib/validate.js#L17

[srinivasiyer]

Hi Catalina,

Thanks for pointing the issue. It was an oversight from my end. I shall try and come up with a fix in a couple of days.

Appreciate the help.