mutationWithClientMutationId should accepts a thunk as outputFilelds

[davide-ganito]

Hi everyone,
I think that mutationWithClientMutationId should accepts also a thunk as outputFilelds.
I need to create payloads with type which are not ready at definition time.

[dschafer]

Yep, good idea; it should take either a thunk or an array!

[dschafer]

Yep, good idea; it should take either a thunk or an array!

I meant thunk or object. Too much time in PHP!

[dschafer]

Should be fixed by #26.