Changed job.commit.body to render on iPhone

The job.config.body element was a pre element and that did not allow it
to wrap on small screens. Also the min-width was greater than the
containing element width.

Fixes: https://github.com/travis-ci/travis-web/issues/285

I do not know the design that lead to using pre in the job.commit.body, so I may well
be breaking some design guidelines here.