Make PubSubAsyncIterator pushQueue protected

[bisztray]

This is more like a very simple feature request then an issue. I'd like to implement a mechanism in the PubSubAsyncIterator to limit the pushQueue size. I'd like to subclass PubSubAsyncIterator but I'd need the pushQueue() function and the pushQueue array to be protected not private.
Is there any reason they are private? If not could you change these, or should I send a pull request?

[chdanielmueller]

It is an implementation of this: https://github.com/apollographql/graphql-subscriptions/blob/master/src/pubsub-async-iterable-iterator.ts

There it is made private.
I do not know if there are reasons for this, I just used the generic sample as provided.