fix(docs): name of callback actor's 2nd argument
fix(docs): name of callback actor's 2nd argument

Just a tiny error: Actor doc refers to callback actor's  2nd argument as `onReceive`, but it is `onEvent` in the linked entry about invoking callback ([link](https://xstate.js.org/docs/guides/communication.html#invoking-callbacks))
davidkpiano/xstate,davidkpiano/xstate,davidkpiano/xstate