`find` is executed even when only `count` is requested

[yoadsn]

This issue was split off from #4 since it represents a separate concern.

In short, even if the requested connection query contains only the count field:

query {
  someConnection {
    count
  }
}

A find would be executed against the target collection.

Suggestion from the original issue: (by @nodkz)

"But we should be sure that in resolveParams.projection do not present extended/defined by wrappers by a developer. So I thought that it is a complicated task.
I think that your suggestion is awesome! If in projection present only count field - we may safely avoiding a find.

It should be realized somehow like countPromise https://github.com/nodkz/graphql-compose-connection/blob/86ddc88dcce544e1579494072c5d7fb72ffad44a/src/connectionResolver.js#L176 and lines 112-118."

This is awaiting a PR to fix.