Expect test server to run on localhost

It seems necessary to set this now that the express app is only listening for connections to localhost.

Author: 36degrees

jest-dev-server.config.js

@@ -5,6 +5,9 @@ const { ports } = require('@govuk-frontend/config')
  */
 module.exports = {
   command: 'npm start --workspace @govuk-frontend/review',
+
+  host: 'localhost',
+
   port: ports.app,
 
   // Allow 30 seconds to start server