Re-add the ERB escaping.
Re-add the ERB escaping.

This was added in bec33e9e9a2a6c673298e69fd88720bc039beaa7, but subsequently disappeared.

robinwhittleton/static,kalleth/static,tadast/static,alphagov/static,kalleth/static,alphagov/static,kalleth/static,robinwhittleton/static,robinwhittleton/static,alphagov/static,robinwhittleton/static,tadast/static,tadast/static,tadast/static,kalleth/static