ui-br-cpf-mask sets model to undefined

I tested it and the other masks seem to work, but the CPF one has something wrong with it. I'm using the 2.6.0 version, which is the latest I found for **bower** (yes unfortunately I'm using it).

This is how I tried using it (the input is wrapped by a form inside a component's template):
```

```

I found, however, a small workaround that has weird behavior sometimes:
```

```

If this has been fixed already, publishing the updated version to bower would really help me out!