Dockerfile with MAINTAINER email fails parsing

`Dockerfile` with `MAINTAINER` with email fails parsing:

```
MAINTAINER Jean Luc Picard <picardj@starfleet.gov>
```

```
[error] Dockerfile: SyntaxError: > must be followed by a word
[error] > 1 | MAINTAINER Jean Luc Picard <picardj@starfleet.gov>
```