Switch to HTTPS for 'Report a problem' links

req.protocol will be HTTP as the Node app itself doesn't know anything
about HTTPS.

Development is the only environment where this would be HTTP, and this
isn't something that we would ever use in dev - so let's just set it
to be HTTPS all the time and be done with it.
Merge pull request #92 from alphagov/report-a-problem-https

Switch to HTTPS for 'Report a problem' links