Wrong number of arguments in moped.rb (aggregate_with_oboe)

We're getting a "wrong number of arguments" in aggregate_with_oboe  for this call to aggregate (using mongoid):

```ruby
    @origin.aggregate(
      {'$match' => query},
      {'$group' => @group},
      {'$project'=> @project},
      {'$out' => collection.name}
    )
```

/abd/app/ev/shared/bundle/ruby/1.9.1/gems/oboe-2.7.5.1/lib/oboe/inst/moped.rb:453:in `aggregate_with_oboe'