Edge case with multiple subscriptions to same query

[darrenclark]

I noticed subscribing to the same GraphQL query twice causes some interesting behaviour. Specifically this happens:

1. client subscribes twice to the exact same query, gets back two responses with same subscriptionId, i.e. "subscriptionId":"__absinthe__:doc:116039402"
2. client receives two subscription:data events (as I'd expect) when changes are published
3. unsubscribing once causes no more subscription:data events for that query, even though I have one "active" subscription

I was wondering what the expected behaviour is? I can try to take a stab at fixing it

Personally, I think it would make sense to require unsubscribing twice (i.e. each doc event for a single query should be paired up with a unsubscribe event)

Thoughts?