decorateHyper should pass through custom children

[mgrip]

From the hyper docs:

We encourage you to maintain compatibility with other decorators. Since many can be set, don't assume that yours is the only one. For example, if you're passing children, compose potential existing values:

render () {
  const customChildren = Array.from(this.props.customChildren)
    .concat(<p>My new child</p>);
  return <Tab {...this.props} customChildren={customChildren} />
}

It looks like the decorateHyper function currently overrides this.props.customChildren rather than appending to it.