Get one definition when there's multiple definitions

Hello, I'm trying to parse this ontology that was recently updated to include Japanese

Source is available from https://raw.githubusercontent.com/EBISPOT/DUO/master/src/ontology/duo-basic.owl

To reproduce the issue, do the following (with pronto installed)

```
from pronto import Ontology
ont = Ontology("https://raw.githubusercontent.com/EBISPOT/DUO/master/src/ontology/duo-basic.owl")
test = ont["DUO:0000019"]
test.definition
```

You will get
```
Definition('当該データを利用して実施した研究の成果を広く科学コミュニティに共有する必要があります')
```

It wasn't an issue before because definition was only written in English, but now, it looks like I will need to check if `lang=en`, the corresponding part of OWL source looks like this


As you can see, I might need to somehow add a flag that checks if `xml:lang="en"`

Thanks so much for the help in advanced!!