message: error when there are conflicting deploy targets at root
diff: @@ -182,7 +182,7 @@ impl Manifest {
  // if there is no environment level deploy target, return the top level deploy target
  let route_config = self.route_config();
  - if route_config.workers_dev_false_by_itself() {
  + if route_config.workers_dev_false_by_itself() || route_config.has_conflicting_targets() {
  failure::bail!("you must set workers_dev = true or provide a zone_id and route/routes.")
  }
  