State challenge links are outdated

[dhcodes]

Since the learnyounode exercises promote the ES6 syntax for React, the documentation links on the State challenge should be updated to reflect this.

Currently, the links are:
Component API: https://facebook.github.io/react/docs/component-api.html
Component Specs and Lifecycle: https://facebook.github.io/react/docs/component-specs.html

But I propose they be changed to:
Setting the Initial State: https://facebook.github.io/react/docs/reusable-components.html#setting-the-initial-state
Autobinding: https://facebook.github.io/react/docs/reusable-components.html#autobinding

I'm happy to open a PR to update this if all agree.

[DusanSacha]

Hi, I know this answers comes a bit late 😄 but PR is always appreciated.