Fix the collections app healthcheck path
Fix the collections app healthcheck path

Topics now live under /topic, and the collections app no longer serves
the unprefixed paths (we've added redirections to the router) so we need
to update the path that the health-check accesses accordingly.

alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet,alphagov/govuk-puppet