CollectionJSON::Attribute ancestors should not (rudely) ignore value fal...

A bug in the CollectionJSON::Attribute class will prevent any attribute (not just 'value', as demonstrated below) from being set to false. But value is one place it really matters.
```
puts CollectionJSON::Data.from_hash(value: false).to_json
```
results in
```
{}
```
whereas
```
CollectionJSON::Data.from_hash(value: true)
```
results in:
```
{"value": true}
```

As far as I can tell, the enclosed patch is a comprehensive solution. All tests pass.