Fix report-a-problem form alignment with new static

On a version of `static` that includes the [report-a-problem improvements](https://github.com/alphagov/static/pull/441),
the report-a-problem form is misaligned:

![image](https://cloud.githubusercontent.com/assets/23801/4057147/d97148f8-2dc4-11e4-8956-de4e9f9fde1e.png)

This change fixes that issue, while not really
breaking anything when `whitehall` runs against the old version of `static`.

/cc @edds @dsingleton