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. This change fixes that issue, while not really
breaking anything when `whitehall` runs against the old version of `static`.
Merge pull request #1686 from alphagov/report-a-problem-styling-with-new-static

Fix report-a-problem form alignment with new static