Feed with last_imported_at and no feed_version_imports

[irees]

This will fail when generating import_status for the serializer:

Started GET "/api/v1/feeds.geojson?onestop_id=f-srb-tperspa" for 127.0.0.1 at 2017-12-04 02:15:58 +0000
Processing by Api::V1::FeedsController#index as GEOJSON
  Parameters: {"onestop_id"=>"f-srb-tperspa"}
Rendered ActiveModel::Serializer::CollectionSerializer with GeoJSONAdapter (4.81ms)
[Unhandled API Exception] [NoMethodError] undefined method `success' for nil:NilClass

See

https://github.com/transitland/transitland/issues/244