Letra V cravada no retorno de método (nahead).

Tanto o método issue_label quanto o issue.label retornam a letra 'v' cravada quando nahead.

```
>>> articledata_xylose = Article(json.loads(client.get_article('S1414-32832016005011101', 'scl')))
>>> 
>>> articledata_xylose.issue_label
u'vnahead'
>>> articledata_xylose.issue.label
u'vnahead'
>>> 
```
