max_results=1 should be honored on aggregation endpoint


### Expected Behavior

When I configure an endpoint with aggregation, I would expect that the response from a get request contains 1 item if I pass `max_results=1` .

### Actual Behavior

Actually the aggregation endpoints return all items (I have only 38 items in the collection) if `max_results` is set to 1.

### Environment

* Python version: 3.7.1 64bit
* Eve version: 0.8.1
