add isFirstRendering property to RouterState interface

[TetsuyaNegishi]

The RouterState interface does not have the isFirstRendering property.
This PR is for adding the isFirstRendering property to the RouterState interface.

[supasate]

Router state in the reducer doesn't have isFirstRendering property. If you intend to to fix it for the payload of LocationChangeAction, it's better to change the RouterState type to a new type composing RouterState.

[TetsuyaNegishi]

Thank you for your feedback!
I Fixed it👍

[supasate]

Thanks for your contribution!