Fix useNavigation params typing

[Aure77]

This fix #49

[slorber]

That was fast 👍

[slorber]

looks good for the specific usecase of params, but for #42 we should also probably remove the hardcoded "NavigationScreenProp" reference because it won't expose the custom navigator actions (like popToTop etc)

I prefer to have one PR fix both the params usecase and custom navigator actions usecases, because if we release a fix for #42 later, we're probably going to break the TS types retrocompatibility so it's likely to be annoying for the users.

[slorber]

We'd rather fix #42 as well, otherwise we'll need to make a breaking change later when fixing #42 (which is likely to annoy you btw because the generics won't work the same way)