rxjs-dev.firebaseapp.com should redirect to rxjs.dev

[tomchen]

https://rxjs-dev.firebaseapp.com/* should obviously redirect to https://rxjs.dev/* (unless the first one is not controlled by the team), to avoid confusion by not only viewers but also search engines - Google kind of doesn't understand rxjs.dev is the primary domain and when you search related terms it gives you rxjs-dev.firebaseapp.com or even other unofficial sites as the first results.

Btw, http://reactivex.io hasn't enabled SSL yet (this issue exists already ReactiveX/reactivex.github.io#389)