<!--**Issue Labels** While not necessary, you can help organize our issues by labeling this issue when you open it. To add a label automatically, simply [x] mark the appropriate box below: - [ ] has-reproduction - [ ] feature - [ ] blocking - [ ] good first issue To add a label not listed above, simply place `/label another-label-name` on a line by itself. --> Shouldn't the return type be `AsyncIterableIterator` ([TS lib file](https://github.com/Microsoft/TypeScript/blob/master/lib/lib.es2018.asynciterable.d.ts#L42)) instead of `AsyncIterator`? I see it has the `Symbol.asyncIterator` property [here](https://github.com/apollographql/graphql-subscriptions/blob/master/src/event-emitter-to-async-iterator.ts#L71)