Revert startup.sh to run rails server
Revert startup.sh to run rails server

Although running unicorn is in many ways an improvement it does cause
some issues (such as breaking better_errors) and it's unlikely to become
consistent quickly across all GOV.UK apps so this is switched back to
using rails server for consistency across GOV.UK.

alphagov/manuals-publisher,alphagov/manuals-publisher,alphagov/manuals-publisher