Use non-null  asset root value in whitehall admin
Use non-null  asset root value in whitehall admin

A null value stops the app from starting due to Plek. This sets it to a
protocol relative URL to the current host so that it will work in both
dev and production without needing a switch for https.

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