fix(types): add lost argument of useStore

[euaaaio]

This PR adds lost argument key to useStore function types.
Resolve #1807

[kiaking]

Thanks for the PR! Yap, this is a defect. However, could you add support for InjectionKey as well as String?
Ref: https://composition-api.vuejs.org/api.html#dependency-injection

So It should be I think?

export function useStore<S = any>(key?: InjectionKey<Store<S>> | string): Store<S>;

[euaaaio]

@kiaking, you're right. I refactored and added a few tests.

[kiaking]

Thanks a lot 🙌