Fix serialization

[cherifGsoul]

To fix a can-reflect issue:

This test should check for deep equality instead of comparing references

This function should be:

serialize: function () {
    if(this._legacyAttrBehavior) {
            return mapHelpers.serialize(this, 'attr', {});
    } else {
           return canReflect.serialize(this, CIDMap);
    }
}