Updating default set

As discussed, in [https://github.com/Financial-Times/polyfill-service/issues/176](issue#176) I have added the following polyfills to the default set:

* Event.DOMContentLoaded
* Event.focusin
* Event.hashchange
* Object.assign
* Object.create
* Object.defineProperties
* Object.defineProperty
* Object.getOwnPropertyNames
* Object.getPrototypeOf
* Object.keys