ack list is always increasing

[nsiitk]

on receiving ack callback is retrieved from the ack[] but the list is always increasing. shouldn't executed cb be removed from ack[]. GCM spec says only 100 pending ack should be there in the ccs and this way can we manage the send message throttle

[nsiitk]

I have changed acks to hash {} and delete acks[msgid] on ack and nack. I can share the code but I am running it with node 12.7 is that ok

[jacobp100]

Should be fine! Send a pr.