PowhegControl: Fixing problem with NNLO reweighting for Hj process

This small patch (4 characters added) should fix a problem reported by @willocq concerning the Hj process. The NNLO reweighting feature was crashing because two parameters were initialised by default to collections.OrderedDict instead of collections.OrderedDict() - i.e. to a type instead of an empty container of that type.